CPU: Difference between revisions
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Rainwarrior (talk | contribs) (→Notes: "kevtris has confirmed..." his work is great but we don't need to treat him like an oracle, others have confirmed this too) |
(PAL NES clones exist) |
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{| class="tabular" | {| class="tabular" | ||
|- | |- | ||
! Rate || NTSC NES/Famicom || PAL NES || PAL Famiclone | ! Rate || NTSC NES/Famicom || PAL NES || PAL Famiclone* | ||
|- | |- | ||
| Color subcarrier frequency ''f{{sub|sc}}'' (exact) || 21477272.<span style="border-top: 1px solid">72</span> Hz (39375000/11 Hz) || 4433618.75 Hz || 4433618.75 Hz | | Color subcarrier frequency ''f{{sub|sc}}'' (exact) || 21477272.<span style="border-top: 1px solid">72</span> Hz (39375000/11 Hz) || 4433618.75 Hz || 4433618.75 Hz | ||
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| CPU clock frequency 6''f{{sub|sc}}''/''d'' || 1.789773 MHz (~559 ns per cycle) || 1.662607 MHz (~601 ns per cycle) || 1.773448 MHz (~564 ns per cycle) | | CPU clock frequency 6''f{{sub|sc}}''/''d'' || 1.789773 MHz (~559 ns per cycle) || 1.662607 MHz (~601 ns per cycle) || 1.773448 MHz (~564 ns per cycle) | ||
|} | |} | ||
<nowiki>*</nowiki> The vast majority of PAL famiclones use this timing. A small number use UMC UA6540+6541, which has PAL NES timing, per a [https://forums.nesdev.org/viewtopic.php?f=3&t=17213#p216082 post by Eugene.S]. | |||
=== Notes === | === Notes === | ||
Revision as of 19:23, 10 January 2019
The NES CPU core is based on the 6502 processor and runs at approximately 1.79 MHz (1.66 MHz in a PAL NES). It is made by Ricoh and lacks the MOS6502's decimal mode. In the NTSC NES, the RP2A03 chip contains the CPU and APU; in the PAL NES, the CPU and APU are contained within the RP2A07 chip.
Sections
- CPU instructions
- CPU addressing modes
- CPU memory map
- CPU power-up state
- CPU registers
- CPU status flag behavior
- CPU interrupts
- Unofficial opcodes
- CPU pin-out and signals, and other hardware pin-outs
CPU signals and frequencies
The CPU generates its clock signal by dividing the master clock signal.
| Rate | NTSC NES/Famicom | PAL NES | PAL Famiclone* |
|---|---|---|---|
| Color subcarrier frequency fsc (exact) | 21477272.72 Hz (39375000/11 Hz) | 4433618.75 Hz | 4433618.75 Hz |
| Color subcarrier frequency fsc (approx.) | 3.579545 MHz | 4.433619 MHz | 4.433619 MHz |
| Master clock frequency 6fsc | 21.477272 MHz | 26.601712 MHz | 26.601712 MHz |
| Clock divisor d | 12 | 16 | 15 |
| CPU clock frequency 6fsc/d | 1.789773 MHz (~559 ns per cycle) | 1.662607 MHz (~601 ns per cycle) | 1.773448 MHz (~564 ns per cycle) |
* The vast majority of PAL famiclones use this timing. A small number use UMC UA6540+6541, which has PAL NES timing, per a post by Eugene.S.
Notes
- All illegal 6502 opcodes execute identically on the 2A03/2A07.
- Every cycle on 6502 is either a read or a write cycle.
- A printer friendly version covering all section is available here.
- Emulator authors may wish to emulate the NTSC NES/Famicom CPU at 21441960 Hz ((341×262-0.5)×4×60) to ensure a synchronised/stable 60 frames per second.[1]
See also
- 2A03 technical reference by Brad Taylor. (Pretty old at this point; information on the wiki might be more up-to-date.)
