User:Karatorian/6502 Instruction Set
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6502 Microprocessor
- Revision 1.02 by _Bnu.
- Revision 1.03 by _Gist.
- Wikification by Karatorian.
Most of the following information has been taking out of the Commodore 64 Programmers Reference Manual simply because it was available in electronic form and there appears to be no difference between this documentation and the 6502 documentation, they are both from the 6500 family after all. I've made changes and additions where appropriate.
In theory you should be able to use any code you can find for emulating the 6510 (the C64 processor).
The Registers Inside The 6502 Microprocessor
Almost all calculations are done in the microprocessor. Registers are special pieces of memory in the processor which are used to carry out, and store information about calculations. The 6502 has the following registers:
The Accumulator
This is the most important register in the microprocessor. Various machine language instructions allow you to copy the contents of a memory location into the accumulator, copy the contents of the accumulator into a memory location, modify the contents of the accumulator or some other register directly, without affecting any memory. And the accumulator is the only register that has instructions for performing math.
The X Index Register
This is a very important register. There are instructions for nearly all of the transformations you can make to the accumulator. But there are other instructions for things that only the X register can do. Various machine language instructions allow you to copy the contents of a memory location into the X register, copy the contents of the X register into a memory location, and modify the contents of the X, or some other register directly.
The Y Index Register
This is a very important register. There are instructions for nearly all of the transformations you can make to the accumulator, and the X register. But there are other instructions for things that only the Y register can do. Various machine language instructions allow you to copy the contents of a memory location into the Y register, copy the contents of the Y register into a memory location, and modify the contents of the Y, or some other register directly.
The Status Register
This register consists of eight "flags" (a flag = something that indicates whether something has, or has not occurred). Bits of this register are altered depending on the result of arithmetic and logical operations. These bits are described below:
Bit No. 7 6 5 4 3 2 1 0
S V R B D I Z C
- C – Carry Flag
- This holds the carry out of the most significant bit in any arithmetic operation. In subtraction operations however, this flag is cleared—set to 0—if a borrow is required, set to 1—if no borrow is required. The carry flag is also used in shift and rotate logical operations.
- Z — Zero Flag
- This is set to 1 when any arithmetic or logical operation produces a zero result, and is set to 0 if the result is non-zero.
- I — Interrupt Disable Flag
- This is an interrupt enable/disable flag. If it is set, interrupts are disabled. If it is cleared, interrupts are enabled.
- D — Decimal Mode Flag
- This is the decimal mode status flag. When set, and an Add with Carry or Subtract with Carry instruction is executed, the source values are treated as valid BCD (Binary Coded Decimal, eg. 0x00–0x99 = 0–99) numbers. The result generated is also a BCD number.
- B — Break Flag
- This is set when a software interrupt (BRK instruction) is executed.
- R — Reserved
- Not used. Supposed to be logical 1 at all times.
- V — Overflow Flag
- When an arithmetic operation produces a result too large to be represented in a byte, V is set.
- S — Sign Flag
- This is set if the result of an operation is negative, cleared if positive.
The most commonly used flags are C, Z, V, S.
The Program Counter
This contains the address of the current machine language instruction being executed. Since the operating system is always "RUN"ning in the Commodore VIC-20 (or, for that matter, any computer), the program counter is always changing. It could only be stopped by halting the microprocessor in some way.
The Stack Pointer
This register contains the location of the first empty place on the stack. The stack is used for temporary storage by machine language programs, and by the computer.
Addressing Modes
Instructions need operands to work on. There are various ways of indicating where the processor is to get these operands. The different methods used to do this are called addressing modes. The 6502 offers 11 modes, as described below.
Immediate
In this mode the operand's value is given in the instruction itself. In assembly language this is indicated by "#" before the operand.
eg. LDA #$0A - means "load the accumulator with the hex value 0A"
In machine code different modes are indicated by different codes. So LDA would be translated into different codes depending on the addressing mode.
In this mode, it is: $A9 $0A
Absolute and Zero-page Absolute
In these modes the operands address is given.
eg. LDA $31F6 - (assembler)
$AD $31F6 - (machine code)
If the address is on zero page—i.e. any address where the high byte is 00—only 1 byte is needed for the address. The processor automatically fills the 00 high byte.
eg. LDA $F4
$A5 $F4
Note the different instruction codes for the different modes. Note also that for 2 byte addresses, the low byte is store first,
eg. LDA $31F6 is stored as three bytes in memory, $AD $F6 $31.
Zero-page absolute is usually just called zero-page.
Implied
No operand addresses are required for this mode. They are implied by the instruction.
eg. TAX - (transfer accumulator contents to X-register)
$AA
Accumulator
In this mode the instruction operates on data in the accumulator, so no operands are needed.
eg. LSR - logical bit shift right
$4A
Indexed and Zero-page Indexed
In these modes the address given is added to the value in either the X or Y index register to give the actual address of the operand.
eg. LDA $31F6, Y
$D9 $31F6
LDA $31F6, X
$DD $31F6
Note that the different operation codes determine the index register used. In the zero-page version, you should note that the X and Y registers are not interchangeable. Most instructions which can be used with zero-page indexing do so with X only.
eg. LDA $20, X
$B5 $20
Indirect
This mode applies only to the JMP instruction - JuMP to new location. It is indicated by parenthesis around the operand. The operand is the address of the bytes whose value is the new location.
eg. JMP ($215F)
Assume the following - byte value
$215F $76
$2160 $30
This instruction takes the value of bytes $215F, $2160 and uses that as the address to jump to - i.e. $3076 (remember that addresses are stored with low byte first).
Pre-Indexed Indirect
In this mode a zer0-page address is added to the contents of the X-register to give the address of the bytes holding the address of the operand. The indirection is indicated by parenthesis in assembly language.
eg. LDA ($3E, X)
$A1 $3E
Assume the following - byte value
X-reg. $05
$0043 $15
$0044 $24
$2415 $6E
Then the instruction is executed by:
(i) adding $3E and $05 = $0043 (ii) getting address contained in bytes $0043, $0044 = $2415 (iii) loading contents of $2415 - i.e. $6E - into accumulator
Note a) When adding the 1-byte address and the X-register, wrap around
addition is used - i.e. the sum is always a zero-page address.
eg. FF + 2 = 0001 not 0101 as you might expect.
DON'T FORGET THIS WHEN EMULATING THIS MODE.
b) Only the X register is used in this mode.
Post-Indexed Indirect
In this mode the contents of a zero-page address (and the following byte) give the indirect addressm which is added to the contents of the Y-register to yield the actual address of the operand. Again, inassembly language, the instruction is indicated by parenthesis.
eg. LDA ($4C), Y
Note that the parenthesis are only around the 2nd byte of the instruction since it is the part that does the indirection.
Assume the following - byte value
$004C $00
$004D $21
Y-reg. $05
$2105 $6D
Then the instruction above executes by:
(i) getting the address in bytes $4C, $4D = $2100
(ii) adding the contents of the Y-register = $2105
(111) loading the contents of the byte $2105 - i.e. $6D into the
accumulator.
Note: only the Y-register is used in this mode.
Relative
This mode is used with Branch-on-Condition instructions. It is probably the mode you will use most often. A 1 byte value is added to the program counter, and the program continues execution from that address. The 1 byte number is treated as a signed number - i.e. if bit 7 is 1, the number given byt bits 0-6 is negative; if bit 7 is 0, the number is positive. This enables a branch displacement of up to 127 bytes in either direction.
eg bit no. 7 6 5 4 3 2 1 0 signed value unsigned value
value 1 0 1 0 0 1 1 1 -39 $A7
value 0 0 1 0 0 1 1 1 +39 $27
Instruction example:
BEQ $A7 $F0 $A7
This instruction will check the zero status bit. If it is set, 39 decimal will be subtracted from the program counter and execution continues from that address. If the zero status bit is not set, execution continues from the following instruction.
Notes: a) The program counter points to the start of the instruction
after the branch instruction before the branch displacement is added.
Remember to take this into account when calculating displacements.
b) Branch-on-condition instructions work by checking the relevant
status bits in the status register. Make sure that they have been set or
unset as you want them. This is often done using a CMP instruction.
c) If you find you need to branch further than 127 bytes, use the
opposite branch-on-condition and a JMP.
MCS6502 Microprocessor Instruction Set
The following notation applies to this summary:
A Accumulator EOR Logical Exclusive Or
X, Y Index Registers fromS Transfer from Stack
M Memory toS Transfer to Stack
P Processor Status Register -> Transfer to
S Stack Pointer <- Transfer from
/ Change V Logical OR
_ No Change PC Program Counter
+ Add PCH Program Counter High
/\ Logical AND PCL Program Counter Low
- Subtract OPER OPERAND
# IMMEDIATE ADDRESSING MODE
Note: At the top of each table is located in parentheses a reference
number (Ref: XX) which directs the user to that Section in the
MCS6500 Microcomputer Family Programming Manual in which the
instruction is defined and discussed.
ADC — Add memory to accumulator with carry
Operation: A + M + C -> A, C N Z C I D V
/ / / _ _ /
(Ref: 2.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ADC #Oper | 69 | 2 | 2 |
| Zero Page | ADC Oper | 65 | 2 | 3 |
| Zero Page,X | ADC Oper,X | 75 | 2 | 4 |
| Absolute | ADC Oper | 60 | 3 | 4 |
| Absolute,X | ADC Oper,X | 7D | 3 | 4* |
| Absolute,Y | ADC Oper,Y | 79 | 3 | 4* |
| (Indirect,X) | ADC (Oper,X) | 61 | 2 | 6 |
| (Indirect),Y | ADC (Oper),Y | 71 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
AND — Boolean and memory with accumulator
Operation: A /\ M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | AND #Oper | 29 | 2 | 2 |
| Zero Page | AND Oper | 25 | 2 | 3 |
| Zero Page,X | AND Oper,X | 35 | 2 | 4 |
| Absolute | AND Oper | 2D | 3 | 4 |
| Absolute,X | AND Oper,X | 3D | 3 | 4* |
| Absolute,Y | AND Oper,Y | 39 | 3 | 4* |
| (Indirect,X) | AND (Oper,X) | 21 | 2 | 6 |
| (Indirect,Y) | AND (Oper),Y | 31 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
ASL — Shift left one bit (memory or accumulator)
+-+-+-+-+-+-+-+-+
Operation: C <- |7|6|5|4|3|2|1|0| <- 0
+-+-+-+-+-+-+-+-+ N Z C I D V
/ / / _ _ _
(Ref: 10.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ASL A | 0A | 1 | 2 |
| Zero Page | ASL Oper | 06 | 2 | 5 |
| Zero Page,X | ASL Oper,X | 16 | 2 | 6 |
| Absolute | ASL Oper | 0E | 3 | 6 |
| Absolute, X | ASL Oper,X | 1E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
BCC — Branch on carry clear
N Z C I D V
Operation: Branch on C = 0 _ _ _ _ _ _
(Ref: 4.1.1.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCC Oper | 90 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BCS — Branch on carry set
Operation: Branch on C = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BCS Oper | B0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
BEQ — Branch on result zero
N Z C I D V
Operation: Branch on Z = 1 _ _ _ _ _ _
(Ref: 4.1.1.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BEQ Oper | F0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to next page.
BIT — Test bits in memory with accumulator
Operation: A /\ M, M7 -> N, M6 -> V
Bit 6 and 7 are transferred to the status register. N Z C I D V
If the result of A /\ M is zero then Z = 1, otherwise M7/ _ _ _ M6
Z = 0
(Ref: 4.2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | BIT Oper | 24 | 2 | 3 |
| Absolute | BIT Oper | 2C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
BMI — Branch on result minus
Operation: Branch on N = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | 30 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 1 if branch occurs to different page.
BNE — Branch on result not zero
Operation: Branch on Z = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BMI Oper | D0 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BPL — Branch on result plus
Operation: Branch on N = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BPL Oper | 10 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BRK — Force break
Operation: Forced Interrupt PC + 2 toS P toS N Z C I D V
_ _ _ 1 _ _
(Ref: 9.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | BRK | 00 | 1 | 7 |
+----------------+-----------------------+---------+---------+----------+
1. A BRK command cannot be masked by setting I.
BVC — Branch on overflow clear
Operation: Branch on V = 0 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVC Oper | 50 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
BVS — Branch on overflow set
Operation: Branch on V = 1 N Z C I D V
_ _ _ _ _ _
(Ref: 4.1.1.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Relative | BVS Oper | 70 | 2 | 2* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if branch occurs to same page.
* Add 2 if branch occurs to different page.
CLC — Clear carry flag
Operation: 0 -> C N Z C I D V
_ _ 0 _ _ _
(Ref: 3.0.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLC | 18 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLD — Clear decimal mode
Operation: 0 -> D N A C I D V
_ _ _ _ 0 _
(Ref: 3.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLD | D8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLI — Clear interrupt disable bit
Operation: 0 -> I N Z C I D V
_ _ _ 0 _ _
(Ref: 3.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLI | 58 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CLV — Clear overflow flag
Operation: 0 -> V N Z C I D V
_ _ _ _ _ 0
(Ref: 3.6.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | CLV | B8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
CMP — Compare memory and accumulator
Operation: A - M N Z C I D V
/ / / _ _ _
(Ref: 4.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CMP #Oper | C9 | 2 | 2 |
| Zero Page | CMP Oper | C5 | 2 | 3 |
| Zero Page,X | CMP Oper,X | D5 | 2 | 4 |
| Absolute | CMP Oper | CD | 3 | 4 |
| Absolute,X | CMP Oper,X | DD | 3 | 4* |
| Absolute,Y | CMP Oper,Y | D9 | 3 | 4* |
| (Indirect,X) | CMP (Oper,X) | C1 | 2 | 6 |
| (Indirect),Y | CMP (Oper),Y | D1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
CPX — Compare Memory and Index X
N Z C I D V
Operation: X - M / / / _ _ _
(Ref: 7.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPX *Oper | E0 | 2 | 2 |
| Zero Page | CPX Oper | E4 | 2 | 3 |
| Absolute | CPX Oper | EC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
CPY — Compare memory and index Y
N Z C I D V
Operation: Y - M / / / _ _ _
(Ref: 7.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | CPY *Oper | C0 | 2 | 2 |
| Zero Page | CPY Oper | C4 | 2 | 3 |
| Absolute | CPY Oper | CC | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
DEC — Decrement memory by one
Operation: M - 1 -> M N Z C I D V
/ / _ _ _ _
(Ref: 10.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | DEC Oper | C6 | 2 | 5 |
| Zero Page,X | DEC Oper,X | D6 | 2 | 6 |
| Absolute | DEC Oper | CE | 3 | 6 |
| Absolute,X | DEC Oper,X | DE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
DEX — Decrement index X by one
Operation: X - 1 -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEX | CA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
DEY — Decrement index Y by one
Operation: Y - 1 -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.7)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | DEY | 88 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
EOR — Boolean exclusive or memory with accumulator
Operation: A EOR M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | EOR #Oper | 49 | 2 | 2 |
| Zero Page | EOR Oper | 45 | 2 | 3 |
| Zero Page,X | EOR Oper,X | 55 | 2 | 4 |
| Absolute | EOR Oper | 40 | 3 | 4 |
| Absolute,X | EOR Oper,X | 5D | 3 | 4* |
| Absolute,Y | EOR Oper,Y | 59 | 3 | 4* |
| (Indirect,X) | EOR (Oper,X) | 41 | 2 | 6 |
| (Indirect),Y | EOR (Oper),Y | 51 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
INC — Increment memory by one
N Z C I D V
Operation: M + 1 -> M / / _ _ _ _
(Ref: 10.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | INC Oper | E6 | 2 | 5 |
| Zero Page,X | INC Oper,X | F6 | 2 | 6 |
| Absolute | INC Oper | EE | 3 | 6 |
| Absolute,X | INC Oper,X | FE | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
INX — Increment Index X by one
N Z C I D V
Operation: X + 1 -> X / / _ _ _ _
(Ref: 7.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INX | E8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
INY — Increment Index Y by one
Operation: Y + 1 -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | INY | C8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
JMP — Jump to new location
Operation: (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH (Ref: 4.0.2) _ _ _ _ _ _
(Ref: 9.8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JMP Oper | 4C | 3 | 3 |
| Indirect | JMP (Oper) | 6C | 3 | 5 |
+----------------+-----------------------+---------+---------+----------+
JSR — Jump to new location saving return address
Operation: PC + 2 toS, (PC + 1) -> PCL N Z C I D V
(PC + 2) -> PCH _ _ _ _ _ _
(Ref: 8.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Absolute | JSR Oper | 20 | 3 | 6 |
+----------------+-----------------------+---------+---------+----------+
LDA — Load accumulator with memory
Operation: M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.1.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDA #Oper | A9 | 2 | 2 |
| Zero Page | LDA Oper | A5 | 2 | 3 |
| Zero Page,X | LDA Oper,X | B5 | 2 | 4 |
| Absolute | LDA Oper | AD | 3 | 4 |
| Absolute,X | LDA Oper,X | BD | 3 | 4* |
| Absolute,Y | LDA Oper,Y | B9 | 3 | 4* |
| (Indirect,X) | LDA (Oper,X) | A1 | 2 | 6 |
| (Indirect),Y | LDA (Oper),Y | B1 | 2 | 5* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 if page boundary is crossed.
LDX — Load index X with memory
Operation: M -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.0)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDX #Oper | A2 | 2 | 2 |
| Zero Page | LDX Oper | A6 | 2 | 3 |
| Zero Page,Y | LDX Oper,Y | B6 | 2 | 4 |
| Absolute | LDX Oper | AE | 3 | 4 |
| Absolute,Y | LDX Oper,Y | BE | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
LDY — Load index Y with memory
N Z C I D V
Operation: M -> Y / / _ _ _ _
(Ref: 7.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | LDY #Oper | A0 | 2 | 2 |
| Zero Page | LDY Oper | A4 | 2 | 3 |
| Zero Page,X | LDY Oper,X | B4 | 2 | 4 |
| Absolute | LDY Oper | AC | 3 | 4 |
| Absolute,X | LDY Oper,X | BC | 3 | 4* |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
LSR — Shift right one bit (memory or accumulator)
+-+-+-+-+-+-+-+-+
Operation: 0 -> |7|6|5|4|3|2|1|0| -> C N Z C I D V
+-+-+-+-+-+-+-+-+ 0 / / _ _ _
(Ref: 10.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | LSR A | 4A | 1 | 2 |
| Zero Page | LSR Oper | 46 | 2 | 5 |
| Zero Page,X | LSR Oper,X | 56 | 2 | 6 |
| Absolute | LSR Oper | 4E | 3 | 6 |
| Absolute,X | LSR Oper,X | 5E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
NOP — No operation
N Z C I D V Operation: No Operation (2 cycles) _ _ _ _ _ _ +----------------+-----------------------+---------+---------+----------+ | Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles| +----------------+-----------------------+---------+---------+----------+ | Implied | NOP | EA | 1 | 2 | +----------------+-----------------------+---------+---------+----------+
ORA — Boolean or memory with accumulator
Operation: A V M -> A N Z C I D V
/ / _ _ _ _
(Ref: 2.2.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | ORA #Oper | 09 | 2 | 2 |
| Zero Page | ORA Oper | 05 | 2 | 3 |
| Zero Page,X | ORA Oper,X | 15 | 2 | 4 |
| Absolute | ORA Oper | 0D | 3 | 4 |
| Absolute,X | ORA Oper,X | 10 | 3 | 4* |
| Absolute,Y | ORA Oper,Y | 19 | 3 | 4* |
| (Indirect,X) | ORA (Oper,X) | 01 | 2 | 6 |
| (Indirect),Y | ORA (Oper),Y | 11 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 on page crossing
PHA — Push accumulator on stack
Operation: A toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.5)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHA | 48 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
PHP — Push processor status on stack
Operation: P toS N Z C I D V
_ _ _ _ _ _
(Ref: 8.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PHP | 08 | 1 | 3 |
+----------------+-----------------------+---------+---------+----------+
PLA — Pull accumulator from stack
Operation: A fromS N Z C I D V
_ _ _ _ _ _
(Ref: 8.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLA | 68 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
PLP — Pull processor status from stack
Operation: P fromS N Z C I D V
From Stack
(Ref: 8.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | PLP | 28 | 1 | 4 |
+----------------+-----------------------+---------+---------+----------+
ROL — Rotate one bit left (memory or accumulator)
+------------------------------+
| M or A |
| +-+-+-+-+-+-+-+-+ +-+ |
Operation: +-< |7|6|5|4|3|2|1|0| <- |C| <-+ N Z C I D V
+-+-+-+-+-+-+-+-+ +-+ / / / _ _ _
(Ref: 10.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROL A | 2A | 1 | 2 |
| Zero Page | ROL Oper | 26 | 2 | 5 |
| Zero Page,X | ROL Oper,X | 36 | 2 | 6 |
| Absolute | ROL Oper | 2E | 3 | 6 |
| Absolute,X | ROL Oper,X | 3E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
ROR — Rotate one bit right (memory or accumulator)
+------------------------------+
| |
| +-+ +-+-+-+-+-+-+-+-+ |
Operation: +-> |C| -> |7|6|5|4|3|2|1|0| >-+ N Z C I D V
+-+ +-+-+-+-+-+-+-+-+ / / / _ _ _
(Ref: 10.4)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Accumulator | ROR A | 6A | 1 | 2 |
| Zero Page | ROR Oper | 66 | 2 | 5 |
| Zero Page,X | ROR Oper,X | 76 | 2 | 6 |
| Absolute | ROR Oper | 6E | 3 | 6 |
| Absolute,X | ROR Oper,X | 7E | 3 | 7 |
+----------------+-----------------------+---------+---------+----------+
Note: ROR instruction is available on MCS650X microprocessors after
June, 1976.
RTI — Return from interrupt
N Z C I D V
Operation: P fromS PC fromS From Stack
(Ref: 9.6)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTI | 4D | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
RTS — Return from subroutine
N Z C I D V
Operation: PC fromS, PC + 1 -> PC _ _ _ _ _ _
(Ref: 8.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | RTS | 60 | 1 | 6 |
+----------------+-----------------------+---------+---------+----------+
SBC — Subtract memory from accumulator with borrow
-
Operation: A - M - C -> A N Z C I D V
- / / / _ _ /
Note:C = Borrow (Ref: 2.2.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Immediate | SBC #Oper | E9 | 2 | 2 |
| Zero Page | SBC Oper | E5 | 2 | 3 |
| Zero Page,X | SBC Oper,X | F5 | 2 | 4 |
| Absolute | SBC Oper | ED | 3 | 4 |
| Absolute,X | SBC Oper,X | FD | 3 | 4* |
| Absolute,Y | SBC Oper,Y | F9 | 3 | 4* |
| (Indirect,X) | SBC (Oper,X) | E1 | 2 | 6 |
| (Indirect),Y | SBC (Oper),Y | F1 | 2 | 5 |
+----------------+-----------------------+---------+---------+----------+
* Add 1 when page boundary is crossed.
SEC — Set carry flag
Operation: 1 -> C N Z C I D V
_ _ 1 _ _ _
(Ref: 3.0.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEC | 38 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
SED — Set decimal mode
N Z C I D V
Operation: 1 -> D _ _ _ _ 1 _
(Ref: 3.3.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SED | F8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
SEI — Set interrupt disable status
N Z C I D V
Operation: 1 -> I _ _ _ 1 _ _
(Ref: 3.2.1)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | SEI | 78 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
STA — Store accumulator in memory
Operation: A -> M N Z C I D V
_ _ _ _ _ _
(Ref: 2.1.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STA Oper | 85 | 2 | 3 |
| Zero Page,X | STA Oper,X | 95 | 2 | 4 |
| Absolute | STA Oper | 8D | 3 | 4 |
| Absolute,X | STA Oper,X | 9D | 3 | 5 |
| Absolute,Y | STA Oper, Y | 99 | 3 | 5 |
| (Indirect,X) | STA (Oper,X) | 81 | 2 | 6 |
| (Indirect),Y | STA (Oper),Y | 91 | 2 | 6 |
+----------------+-----------------------+---------+---------+----------+
STX — Store index X in memory
Operation: X -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.2)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STX Oper | 86 | 2 | 3 |
| Zero Page,Y | STX Oper,Y | 96 | 2 | 4 |
| Absolute | STX Oper | 8E | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
STY — Store index Y in memory
Operation: Y -> M N Z C I D V
_ _ _ _ _ _
(Ref: 7.3)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Zero Page | STY Oper | 84 | 2 | 3 |
| Zero Page,X | STY Oper,X | 94 | 2 | 4 |
| Absolute | STY Oper | 8C | 3 | 4 |
+----------------+-----------------------+---------+---------+----------+
TAX — Transfer accumulator to index X
Operation: A -> X N Z C I D V
/ / _ _ _ _
(Ref: 7.11)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAX | AA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TAY — Transfer accumulator to index Y
Operation: A -> Y N Z C I D V
/ / _ _ _ _
(Ref: 7.13)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TAY | A8 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TSX — Transfer stack pointer to index X
Operation: S -> X N Z C I D V
/ / _ _ _ _
(Ref: 8.9)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TSX | BA | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXA — Transfer index X to accumulator
N Z C I D V
Operation: X -> A / / _ _ _ _
(Ref: 7.12)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXA | 8A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TXS — Transfer index X to stack pointer
N Z C I D V
Operation: X -> S _ _ _ _ _ _
(Ref: 8.8)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TXS | 9A | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
TYA — Transfer index Y to accumulator
Operation: Y -> A N Z C I D V
/ / _ _ _ _
(Ref: 7.14)
+----------------+-----------------------+---------+---------+----------+
| Addressing Mode| Assembly Language Form| OP CODE |No. Bytes|No. Cycles|
+----------------+-----------------------+---------+---------+----------+
| Implied | TYA | 98 | 1 | 2 |
+----------------+-----------------------+---------+---------+----------+
Instruction Addressing Modes and Related Execution Times
+------------------------------------------------------------------------ | INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES | (in clock cycles) +------------------------------------------------------------------------
A A A B B B B B B B B B B C
D N S C C E I M N P R V V L
C D L C S Q T I E L K C S C
Accumulator | . . 2 . . . . . . . . . . .
Immediate | 2 2 . . . . . . . . . . .
Zero Page | 3 3 5 . . . 3 . . . . . . .
Zero Page,X | 4 4 6 . . . . . . . . . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | 4 4 6 . . . 4 . . . . . . .
Absolute,X | 4* 4* 7 . . . . . . . . . . .
Absolute,Y | 4* 4* . . . . . . . . . . . .
Implied | . . . . . . . . . . . . . 2
Relative | . . . 2** 2** 2** . 2** 2** 2** 7 2** 2** .
(Indirect,X) | 6 6 . . . . . . . . . . . .
(Indirect),Y | 5* 5* . . . . . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
C C C C C C D D D E I I I J
L L L M P P E E E O N N N M
D I V P X Y C X Y R C X Y P
Accumulator | . . . . . . . . . . . . . .
Immediate | . . . 2 2 2 . . . 2 . . . .
Zero Page | . . . 3 3 3 5 . . 3 5 . . .
Zero Page,X | . . . 4 . . 6 . . 4 6 . . .
Zero Page,Y | . . . . . . . . . . . . . .
Absolute | . . . 4 4 4 6 . . 4 6 . . 3
Absolute,X | . . . 4* . . 7 . . 4* 7 . . .
Absolute,Y | . . . 4* . . . . . 4* . . . .
Implied | 2 2 2 . . . . 2 2 . . 2 2 .
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . . . 6 . . . . . 6 . . . .
(Indirect),Y | . . . 5* . . . . . 5* . . . .
Abs. Indirect| . . . . . . . . . . . . . 5
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
------------------------------------------------------------------------+ INSTRUCTION ADDRESSING MODES AND RELATED EXECUTION TIMES | (in clock cycles) | ------------------------------------------------------------------------+
J L L L L N O P P P P R R R
S D D D S O R H H L L O O T
R A X Y R P A A P A P L R I
Accumulator | . . . . 2 . . . . . . 2 2 .
Immediate | . 2 2 2 . . 2 . . . . . . .
Zero Page | . 3 3 3 5 . 3 . . . . 5 5 .
Zero Page,X | . 4 . 4 6 . 4 . . . . 6 6 .
Zero Page,Y | . . 4 . . . . . . . . . . .
Absolute | 6 4 4 4 6 . 4 . . . . 6 6 .
Absolute,X | . 4* . 4* 7 . 4* . . . . 7 7 .
Absolute,Y | . 4* 4* . . . 4* . . . . . . .
Implied | . . . . . 2 . 3 3 4 4 . . 6
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . . 6 . . . . . . .
(Indirect),Y | . 5* . . . . 5* . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
R S S S S S S S T T T T T T
T B E E E T T T A A S X X Y
S C C D I A X Y X Y X A S A
Accumulator | . . . . . . . . . . . . . .
Immediate | . 2 . . . . . . . . . . . .
Zero Page | . 3 . . . 3 3 3 . . . . . .
Zero Page,X | . 4 . . . 4 . 4 . . . . . .
Zero Page,Y | . . . . . . 4 . . . . . . .
Absolute | . 4 . . . 4 4 4 . . . . . .
Absolute,X | . 4* . . . 5 . . . . . . . .
Absolute,Y | . 4* . . . 5 . . . . . . . .
Implied | 6 . 2 2 2 . . . 2 2 2 2 2 2
Relative | . . . . . . . . . . . . . .
(Indirect,X) | . 6 . . . 6 . . . . . . . .
(Indirect),Y | . 5* . . . 6 . . . . . . . .
Abs. Indirect| . . . . . . . . . . . . . .
+-----------------------------------------------------------
* Add one cycle if indexing across page boundary
** Add one cycle if branch is taken, Add one additional if branching
operation crosses page boundary
00 - BRK 20 - JSR
01 - ORA - (Indirect,X) 21 - AND - (Indirect,X)
02 - Future Expansion 22 - Future Expansion
03 - Future Expansion 23 - Future Expansion
04 - Future Expansion 24 - BIT - Zero Page
05 - ORA - Zero Page 25 - AND - Zero Page
06 - ASL - Zero Page 26 - ROL - Zero Page
07 - Future Expansion 27 - Future Expansion
08 - PHP 28 - PLP
09 - ORA - Immediate 29 - AND - Immediate
0A - ASL - Accumulator 2A - ROL - Accumulator
0B - Future Expansion 2B - Future Expansion
0C - Future Expansion 2C - BIT - Absolute
0D - ORA - Absolute 2D - AND - Absolute
0E - ASL - Absolute 2E - ROL - Absolute
0F - Future Expansion 2F - Future Expansion
10 - BPL 30 - BMI
11 - ORA - (Indirect),Y 31 - AND - (Indirect),Y
12 - Future Expansion 32 - Future Expansion
13 - Future Expansion 33 - Future Expansion
14 - Future Expansion 34 - Future Expansion
15 - ORA - Zero Page,X 35 - AND - Zero Page,X
16 - ASL - Zero Page,X 36 - ROL - Zero Page,X
17 - Future Expansion 37 - Future Expansion
18 - CLC 38 - SEC
19 - ORA - Absolute,Y 39 - AND - Absolute,Y
1A - Future Expansion 3A - Future Expansion
1B - Future Expansion 3B - Future Expansion
1C - Future Expansion 3C - Future Expansion
1D - ORA - Absolute,X 3D - AND - Absolute,X
1E - ASL - Absolute,X 3E - ROL - Absolute,X
1F - Future Expansion 3F - Future Expansion
40 - RTI 60 - RTS
41 - EOR - (Indirect,X) 61 - ADC - (Indirect,X)
42 - Future Expansion 62 - Future Expansion
43 - Future Expansion 63 - Future Expansion
44 - Future Expansion 64 - Future Expansion
45 - EOR - Zero Page 65 - ADC - Zero Page
46 - LSR - Zero Page 66 - ROR - Zero Page
47 - Future Expansion 67 - Future Expansion
48 - PHA 68 - PLA
49 - EOR - Immediate 69 - ADC - Immediate
4A - LSR - Accumulator 6A - ROR - Accumulator
4B - Future Expansion 6B - Future Expansion
4C - JMP - Absolute 6C - JMP - Indirect
4D - EOR - Absolute 6D - ADC - Absolute
4E - LSR - Absolute 6E - ROR - Absolute
4F - Future Expansion 6F - Future Expansion
50 - BVC 70 - BVS
51 - EOR - (Indirect),Y 71 - ADC - (Indirect),Y
52 - Future Expansion 72 - Future Expansion
53 - Future Expansion 73 - Future Expansion
54 - Future Expansion 74 - Future Expansion
55 - EOR - Zero Page,X 75 - ADC - Zero Page,X
56 - LSR - Zero Page,X 76 - ROR - Zero Page,X
57 - Future Expansion 77 - Future Expansion
58 - CLI 78 - SEI
59 - EOR - Absolute,Y 79 - ADC - Absolute,Y
5A - Future Expansion 7A - Future Expansion
5B - Future Expansion 7B - Future Expansion
5C - Future Expansion 7C - Future Expansion
5D - EOR - Absolute,X 7D - ADC - Absolute,X
5E - LSR - Absolute,X 7E - ROR - Absolute,X
5F - Future Expansion 7F - Future Expansion
80 - Future Expansion A0 - LDY - Immediate
81 - STA - (Indirect,X) A1 - LDA - (Indirect,X)
82 - Future Expansion A2 - LDX - Immediate
83 - Future Expansion A3 - Future Expansion
84 - STY - Zero Page A4 - LDY - Zero Page
85 - STA - Zero Page A5 - LDA - Zero Page
86 - STX - Zero Page A6 - LDX - Zero Page
87 - Future Expansion A7 - Future Expansion
88 - DEY A8 - TAY
89 - Future Expansion A9 - LDA - Immediate
8A - TXA AA - TAX
8B - Future Expansion AB - Future Expansion
8C - STY - Absolute AC - LDY - Absolute
8D - STA - Absolute AD - LDA - Absolute
8E - STX - Absolute AE - LDX - Absolute
8F - Future Expansion AF - Future Expansion
90 - BCC B0 - BCS
91 - STA - (Indirect),Y B1 - LDA - (Indirect),Y
92 - Future Expansion B2 - Future Expansion
93 - Future Expansion B3 - Future Expansion
94 - STY - Zero Page,X B4 - LDY - Zero Page,X
95 - STA - Zero Page,X B5 - LDA - Zero Page,X
96 - STX - Zero Page,Y B6 - LDX - Zero Page,Y
97 - Future Expansion B7 - Future Expansion
98 - TYA B8 - CLV
99 - STA - Absolute,Y B9 - LDA - Absolute,Y
9A - TXS BA - TSX
9B - Future Expansion BB - Future Expansion
9C - Future Expansion BC - LDY - Absolute,X
9D - STA - Absolute,X BD - LDA - Absolute,X
9E - Future Expansion BE - LDX - Absolute,Y
9F - Future Expansion BF - Future Expansion
C0 - Cpy - Immediate E0 - CPX - Immediate
C1 - CMP - (Indirect,X) E1 - SBC - (Indirect,X)
C2 - Future Expansion E2 - Future Expansion
C3 - Future Expansion E3 - Future Expansion
C4 - CPY - Zero Page E4 - CPX - Zero Page
C5 - CMP - Zero Page E5 - SBC - Zero Page
C6 - DEC - Zero Page E6 - INC - Zero Page
C7 - Future Expansion E7 - Future Expansion
C8 - INY E8 - INX
C9 - CMP - Immediate E9 - SBC - Immediate
CA - DEX EA - NOP
CB - Future Expansion EB - Future Expansion
CC - CPY - Absolute EC - CPX - Absolute
CD - CMP - Absolute ED - SBC - Absolute
CE - DEC - Absolute EE - INC - Absolute
CF - Future Expansion EF - Future Expansion
D0 - BNE F0 - BEQ
D1 - CMP (Indirect),Y F1 - SBC - (Indirect),Y
D2 - Future Expansion F2 - Future Expansion
D3 - Future Expansion F3 - Future Expansion
D4 - Future Expansion F4 - Future Expansion
D5 - CMP - Zero Page,X F5 - SBC - Zero Page,X
D6 - DEC - Zero Page,X F6 - INC - Zero Page,X
D7 - Future Expansion F7 - Future Expansion
D8 - CLD F8 - SED
D9 - CMP - Absolute,Y F9 - SBC - Absolute,Y
DA - Future Expansion FA - Future Expansion
DB - Future Expansion FB - Future Expansion
DC - Future Expansion FC - Future Expansion
DD - CMP - Absolute,X FD - SBC - Absolute,X
DE - DEC - Absolute,X FE - INC - Absolute,X
DF - Future Expansion FF - Future Expansion
Instruction Operation
The following code has been taken from VICE for the purposes of showing how each instruction operates. No particular addressing mode is used since we only wish to see the operation of the instruction itself.
src : the byte of data that is being addressed.
SET_SIGN : sets\resets the sign flag depending on bit 7.
SET_ZERO : sets\resets the zero flag depending on whether the result
is zero or not.
SET_CARRY(condition) : if the condition has a non-zero value then the
carry flag is set, else it is reset.
SET_OVERFLOW(condition) : if the condition is true then the overflow
flag is set, else it is reset.
SET_INTERRUPT : }
SET_BREAK : } As for SET_CARRY and SET_OVERFLOW.
SET_DECIMAL : }
REL_ADDR(PC, src) : returns the relative address obtained by adding
the displacement src to the PC.
SET_SR : set the Program Status Register to the value given.
GET_SR : get the value of the Program Status Register.
PULL : Pull a byte off the stack.
PUSH : Push a byte onto the stack.
LOAD : Get a byte from the memory address.
STORE : Store a byte in a memory address.
IF_CARRY, IF_OVERFLOW, IF_SIGN, IF_ZERO etc : Returns true if the
relevant flag is set, otherwise returns false.
clk : the number of cycles an instruction takes. This is shown below
in situations where the number of cycles changes depending
on the result of the instruction (eg. Branching instructions).
AC = Accumulator
XR = X register
YR = Y register
PC = Program Counter
SP = Stack Pointer
/* ADC */
unsigned int temp = src + AC + (IF_CARRY() ? 1 : 0);
SET_ZERO(temp & 0xff); /* This is not valid in decimal mode */
if (IF_DECIMAL()) {
if (((AC & 0xf) + (src & 0xf) + (IF_CARRY() ? 1 : 0)) > 9) temp += 6;
SET_SIGN(temp);
SET_OVERFLOW(!((AC ^ src) & 0x80) && ((AC ^ temp) & 0x80));
if (temp > 0x99) temp += 96;
SET_CARRY(temp > 0x99);
} else {
SET_SIGN(temp);
SET_OVERFLOW(!((AC ^ src) & 0x80) && ((AC ^ temp) & 0x80));
SET_CARRY(temp > 0xff);
}
AC = ((BYTE) temp);
/* AND */
src &= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* ASL */
SET_CARRY(src & 0x80);
src <<= 1;
src &= 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* BCC */
if (!IF_CARRY()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BCS */
if (IF_CARRY()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BEQ */
if (IF_ZERO()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BIT */
SET_SIGN(src);
SET_OVERFLOW(0x40 & src); /* Copy bit 6 to OVERFLOW flag. */
SET_ZERO(src & AC);
/* BMI */
if (IF_SIGN()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BNE */
if (!IF_ZERO()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BPL */
if (!IF_SIGN()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BRK */
PC++;
PUSH((PC >> 8) & 0xff); /* Push return address onto the stack. */
PUSH(PC & 0xff);
SET_BREAK((1)); /* Set BFlag before pushing */
PUSH(SR);
SET_INTERRUPT((1));
PC = (LOAD(0xFFFE) | (LOAD(0xFFFF) << 8));
/* BVC */
if (!IF_OVERFLOW()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* BVS */
if (IF_OVERFLOW()) {
clk += ((PC & 0xFF00) != (REL_ADDR(PC, src) & 0xFF00) ? 2 : 1);
PC = REL_ADDR(PC, src);
}
/* CLC */
SET_CARRY((0));
/* CLD */
SET_DECIMAL((0));
/* CLI */
SET_INTERRUPT((0));
/* CLV */
SET_OVERFLOW((0));
/* CMP */
src = AC - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* CPX */
src = XR - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* CPY */
src = YR - src;
SET_CARRY(src < 0x100);
SET_SIGN(src);
SET_ZERO(src &= 0xff);
/* DEC */
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE(address, (src));
/* DEX */
unsigned src = XR;
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* DEY */
unsigned src = YR;
src = (src - 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* EOR */
src ^= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* INC */
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE(address, (src));
/* INX */
unsigned src = XR;
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* INY */
unsigned src = YR;
src = (src + 1) & 0xff;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* JMP */
PC = (src);
/* JSR */
PC--;
PUSH((PC >> 8) & 0xff); /* Push return address onto the stack. */
PUSH(PC & 0xff);
PC = (src);
/* LDA */
SET_SIGN(src);
SET_ZERO(src);
AC = (src);
/* LDX */
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* LDY */
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* LSR */
SET_CARRY(src & 0x01);
src >>= 1;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* NOP */
Nothing.
/* ORA */
src |= AC;
SET_SIGN(src);
SET_ZERO(src);
AC = src;
/* PHA */
src = AC;
PUSH(src);
/* PHP */
src = GET_SR;
PUSH(src);
/* PLA */
src = PULL();
SET_SIGN(src); /* Change sign and zero flag accordingly. */
SET_ZERO(src);
/* PLP */
src = PULL();
SET_SR((src));
/* ROL */
src <<= 1;
if (IF_CARRY()) src |= 0x1;
SET_CARRY(src > 0xff);
src &= 0xff;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* ROR */
if (IF_CARRY()) src |= 0x100;
SET_CARRY(src & 0x01);
src >>= 1;
SET_SIGN(src);
SET_ZERO(src);
STORE src in memory or accumulator depending on addressing mode.
/* RTI */
src = PULL();
SET_SR(src);
src = PULL();
src |= (PULL() << 8); /* Load return address from stack. */
PC = (src);
/* RTS */
src = PULL();
src += ((PULL()) << 8) + 1; /* Load return address from stack and add 1. */
PC = (src);
/* SBC */
unsigned int temp = AC - src - (IF_CARRY() ? 0 : 1);
SET_SIGN(temp);
SET_ZERO(temp & 0xff); /* Sign and Zero are invalid in decimal mode */
SET_OVERFLOW(((AC ^ temp) & 0x80) && ((AC ^ src) & 0x80));
if (IF_DECIMAL()) {
if ( ((AC & 0xf) - (IF_CARRY() ? 0 : 1)) < (src & 0xf)) /* EP */ temp -= 6;
if (temp > 0x99) temp -= 0x60;
}
SET_CARRY(temp < 0x100);
AC = (temp & 0xff);
/* SEC */
SET_CARRY((1));
/* SED */
SET_DECIMAL((1));
/* SEI */
SET_INTERRUPT((1));
/* STA */
STORE(address, (src));
/* STX */
STORE(address, (src));
/* STY */
STORE(address, (src));
/* TAX */
unsigned src = AC;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* TAY */
unsigned src = AC;
SET_SIGN(src);
SET_ZERO(src);
YR = (src);
/* TSX */
unsigned src = SP;
SET_SIGN(src);
SET_ZERO(src);
XR = (src);
/* TXA */
unsigned src = XR;
SET_SIGN(src);
SET_ZERO(src);
AC = (src);
/* TXS */
unsigned src = XR;
SP = (src);
/* TYA */
unsigned src = YR;
SET_SIGN(src);
SET_ZERO(src);
AC = (src);
Summary of 6502 Opcodes
ADC Add to accumulator with carry. AND "AND" with accumulator. ASL Arithmetic Shift Left. Bit0=0 C=Bit7. BCC Branch on Carry Clear. BCS Branch on Carry Set. BEQ Branch on result Equal (zero). BIT Test bits in memory with accumulator. BMI Branch on result Minus. BNE Branch on result Not Equal (not zero). BPL Branch on result Plus. BRK Forced BREAK. BVC Branch on overflow Clear. BVS Branch on overflow Set. CLC Clear Carry flag. CLD Clear Decimal mode. CLI Clear Interrupt disable bit. CLV Clear overflow flag. CMP Compare with accumulator. CPX Compare with X register. CPY Compare with Y register. DEC Decrement memory by one. DEX Decrement X register by one. DEY Decrement Y register by one. EOR "Exclusive-OR" with accumulator. INC Increment memory by one. INX Increment X register by one. INY Increment Y register by one. JMP Unconditional Jump to new address. JSR Unconditional Jump, saving return address. LDA Load accumulator. LDX Load X register. LDY Load Y register. LSR Logical Shift Right. Bit7=0 C=Bit0. NOP No Operation. ORA "OR" with accumulator. PHA Push Accumulator on stack. PHP Push Processor status register on stack. PLA Pull Accumulator from stack. PLP Pull Processor status register from stack. ROL Rotate one bit Left (mem. or acc.). C=Bit7 Bit0=C. ROR Rotate one bit Right (mem. or acc.). C=Bit0 Bit7=C. RTI Return from Interrupt. RTS Return from Subroutine. SBC Subtract from accumulator with borrow. SEC Set Carry flag. SED Set Decimal mode. SEI Set Interrupt disable status. STA Store Accumulator in memory. STX Store X register in memory. STY Store Y register in memory. TAX Transfer Accumulator to X register. TAY Transfer Accumulator to Y register. TSX Transfer Stack pointer to X register. TXA Transfer X register to Accumulator. TXS Transfer X register to Stack pointer. TYA Transfer Y register to Accumulator. The Processor Status Register, "P" --- --------- ------ --------- --- 7 6 5 4 3 2 1 0 N V B D I Z C 7 N Negative 6 V Overflow 5 <..Future expansion..> 4 B BRK command 3 D Decimal mode 2 I IRQ disable 1 Z Zero 0 C Carry Addressing Modes of 6502 Assembly Code ---------- ----- -- ---- -------- ---- LDA #$07 Immediate mode LDA $1F Zero page absolute LDA $0800 Absolute CLC Implied JMP ($0036) Indirect absolute LDA $FE90,X Absolute indexed (by X) LDA $FE90,Y Absolute indexed (by Y) LDA $2A,X Zero page indexed LDA ($2A,X) Indexed indirect LDA ($2A),Y Indirect indexed BCC $03 Relative BCC $0803 Relative (alternate form) LSR A Accumulator LSR Accumulator (alternate form)
