CPU pinout
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Pin out
| AD1 - 01 | 40 - +5V |
| AD2 - 02 | 39 - STR |
| /RST - 03 | 38 - E44 |
| A00 - 04 | 37 - E45 |
| A01 - 05 | 36 - /OE1 |
| A02 - 06 | 35 - /OE2 |
| A03 - 07 | 34 - R/W |
| A04 - 08 | 33 - NMI |
| A05 - 09 | 32 - /IRQ |
| A06 - 10 | 31 - M2 |
| A07 - 11 | 30 - IOE (usually GND) |
| A08 - 12 | 29 - CLK |
| A09 - 13 | 28 - D0 |
| A10 - 14 | 27 - D1 |
| A11 - 15 | 26 - D2 |
| A12 - 16 | 25 - D3 |
| A13 - 17 | 24 - D4 |
| A14 - 18 | 23 - D5 |
| A15 - 19 | 22 - D6 |
| GND - 20 | 21 - D7 |
Signal description
Active-Low signals are indicated by a "/".
- CLK is the 21.47727 MHz clock input. Internally, the real clock is derived by dividing the input clock frequency by 12.
- AD1 and AD2 are the Audio Out pins.
- Axx is the address bus and Dx the data bus.
- STR stands for "strobe" and goes to the controller ports ($4016 output latch bit 0), D0 on the controller port pinout
- /OE1 and /OE2 also go to the controller ports, and each enable the output of their respective controller, if present.
- E44 and E45 are respectively the expansion port pins 44 and 45 and latched copies of bits 1 and 2 written to $4016
- R/W is the read/write signal, which is used to indicate operations of the same names. Low is write.
- /NMI and /IRQ are the two interrupt pins. See the 6502 manual for more detailed explanation.
- M2 can be considered as a "signals ready" pin. It is actually a delayed form of CLK. In 6502 documentation it's called φ2
- IOE (tentative name) (pin 30) is special: normally it is grounded in the NES, Famicom, PC10/VS. NES and other Nintendo Arcade Boards (Popeye and Donkey Kong 3), but if it is pulled high, all of the memory-mapped I/O ports (APU/Serial Controller area at $4000-$4015) are disabled, and the chip acts like a 'normal' 6502, just without decimal mode and with the pinout and clock divider of an RP2A03/RP2A07. (What effect does this have on PPU ports at $2000-$3FFF and $4016/$4017?)
