CPU: Difference between revisions

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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 [http://en.wikipedia.org/wiki/Ricoh Ricoh] and lacks the MOS6502's decimal mode. In the NTSC NES, the [http://en.wikipedia.org/wiki/Ricoh_2A03 RP2A03] chip contains the CPU and APU; in the PAL NES, the CPU and APU are contained within the [http://en.wikipedia.org/wiki/Ricoh_2A03 RP2A07] chip.  
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 [http://en.wikipedia.org/wiki/Ricoh Ricoh] and lacks the MOS6502's decimal mode. In the NTSC NES, the [http://en.wikipedia.org/wiki/Ricoh_2A03 RP2A03] chip contains the CPU and APU; in the PAL NES, the CPU and APU are contained within the [http://en.wikipedia.org/wiki/Ricoh_2A03 RP2A07] chip.  


=== Sections ===
== Sections ==
* [[6502 instructions|CPU instructions]]
* [[6502 instructions|CPU instructions]]
* [[CPU addressing modes]]
* [[CPU addressing modes]]
* [[CPU memory map]]
* [[CPU memory map]]
* [[CPU_power_up_state|CPU power-up state]]
* [[CPU power up state|CPU power-up state]]
* [[CPU registers]]
* [[CPU registers]]
* [[CPU status flag behavior]]
* [[CPU status flag behavior]]
* [[CPU interrupts]]
* [[CPU interrupts]]
* [[CPU unofficial opcodes|Unofficial opcodes]]
* [[CPU unofficial opcodes|Unofficial opcodes]]
* [[CPU_pin_out_and_signal_description|CPU pin-out and signals]], and other [[hardware pinout|hardware pin-outs]]
* [[CPU pinout|CPU pin-out and signals]], and other [[hardware pinout|hardware pin-outs]]


=== CPU signals and frequencies ===
== Frequencies ==
The CPU generates its clock signal by dividing the master clock signal.
The CPU generates its clock signal by dividing the master clock signal.
{| class="tabular"
{| class="tabular"
|-
|-
! Rate || NTSC NES/Famicom || PAL NES || PAL Famiclone
! Rate || NTSC NES/Famicom || PAL NES || Dendy
|-
|-
| 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) || 3579545.<span style="text-decoration:overline;">45</span> Hz (315/88 MHz) || 4433618.75 Hz || 4433618.75 Hz
|-
|-
| Color subcarrier frequency ''f{{sub|sc}}'' (approx.) || 3.579545 MHz || 4.433619 MHz || 4.433619 MHz
| Color subcarrier frequency ''f{{sub|sc}}'' (approx.) || 3.579545 MHz || 4.433619 MHz || 4.433619 MHz
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|}
|}


=== Notes ===  
<nowiki>*</nowiki> The vast majority of PAL famiclones use a chipset or NOAC with this timing. A small number have UMC UA6540+6541, which also uses PAL NES timing.<ref>[https://forums.nesdev.org/viewtopic.php?f=3&t=17213#p216082 nesdev forum: Eugene.S provides a list of famiclones]</ref>
* Kevtris has confirmed that all illegal 6502 opcodes execute identically on the 2A03/2A07. He has even went as far as to integrate them into the CopyNES BIOS.
 
== Notes ==
* All illegal 6502 opcodes execute identically on the 2A03/2A07.
* Every cycle on 6502 is either a read or a write cycle.
* Every cycle on 6502 is either a read or a write cycle.
* A printer friendly version covering all section is available [[CPU ALL|here]].
* A printer friendly version covering all section is available [[CPU ALL|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.<ref>[http://forums.nesdev.org/viewtopic.php?p=223679#p223679 nesdev forum: Mesen - NES Emulator]</ref>


=== See also ===
== See also ==
* [[Cycle reference chart]]
* [http://nesdev.org/2A03%20technical%20reference.txt 2A03 technical reference] by Brad Taylor. (Pretty old at this point; information on the wiki might be more up-to-date.)


* [http://nesdev.org/2A03%20technical%20reference.txt 2A03 technical reference] by Brad Taylor. (Pretty old at this point; information on the wiki might be more up-to-date.)
== References ==
<references/>

Latest revision as of 05:35, 11 January 2023

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

Frequencies

The CPU generates its clock signal by dividing the master clock signal.

Rate NTSC NES/Famicom PAL NES Dendy
Color subcarrier frequency fsc (exact) 3579545.45 Hz (315/88 MHz) 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 a chipset or NOAC with this timing. A small number have UMC UA6540+6541, which also uses PAL NES timing.[1]

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.[2]

See also

References