CPU pinout: Difference between revisions

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=== Signal description ===  
=== Signal description ===  
Active-Low signals are indicated by a "/". Every cycle is either a read or a write cycle.


* CLK is the 21.47727 MHz (NTSC) or 26.6017 MHz (PAL) clock input. Internally, this clock is divided by 12 (NTSC 2A03) or 16 (PAL 2A07) to feed the 6502's clock input φ0, which is in turn inverted to form φ1, which is then inverted to form φ2. φ1 is high during the first '''p'''hase (half-cycle) of each CPU cycle, while φ2 is high during the second '''p'''hase - hence the names.
{{mbox
* AD1 (both pulse waves) and AD2 (triangle, noise, and DPCM) are the Audio Out pins.
| type = notice
* Axx is the address bus and Dx the data bus. Axx holds the target address during the entire read/write cycle. For reads, the value is read from Dx during φ2. For writes, the value appears on Dx during φ2 (and no sooner).
| text = '''Active-Low signals are prefixed by a / (slash) symbol. Every cycle is either a read or a write cycle.'''
* OUT0-OUT2 are output pins used by the controllers ($4016 output latch bits 0-2). These 3 pins are connected to either the [[NES expansion port pinout|NES's]] or [[Famicom expansion port pinout|Famicom's]] expansion port, and OUT0 is additionally used as the "strobe" signal (OUT) on both [[controller port pinout|controller ports]].
}}
* /OE1 and /OE2 also go to the controller ports, and each enable the output of their respective controller, if present.
 
* R/W is the read/write signal, which is used to indicate operations of the same names. Low is write. R/W stays high/low during the entire read/write cycle.
* '''CLK''' : 21.47727 MHz (NTSC) or 26.6017 MHz (PAL) clock input. Internally, this clock is divided by 12 (NTSC [[CPU|2A03]]) or 16 (PAL [[CPU|2A07]]) to feed the 6502's clock input φ0, which is in turn inverted to form φ1, which is then inverted to form φ2. φ1 is high during the first phase (half-cycle) of each CPU cycle, while φ2 is high during the second phase.
* /NMI and /IRQ are the two interrupt pins. See the 6502 manual and [[CPU interrupts]] for more details.
* '''AD1''' : Audio out pin (both pulse waves).
* M2 can be considered as a "signals ready" pin. It is a modified version the 6502's φ2 (which roughly corresponds to the CPU input clock φ0) that allows for slower ROMs. CPU cycles begin at the point where M2 goes low.
* '''AD2''' : Audio out pin (triangle, noise, and DPCM).
** In the NTSC 2A03, M2 has a [[Glossary|duty cycle]] of 5/8th, or 350ns/559ns. Equivalently, a CPU read (which happens during the second, high phase of M2) takes 1 and 7/8th PPU cycles. The internal φ2 duty cycle is exactly 1/2 (one half).
* '''Axx''' and '''Dx''' : Address and data bus, respectively. '''Axx''' holds the target address during the entire read/write cycle. For reads, the value is read from '''Dx''' during φ2. For writes, the value appears on '''Dx''' during φ2 (and no sooner).
* '''OUT0..OUT2''' : Output pins used by the controllers ($4016 output latch bits 0-2). These 3 pins are connected to either the [[NES expansion port pinout|NES]] or [[Famicom expansion port pinout|Famicom's]] expansion port, and '''OUT0''' is additionally used as the "strobe" signal (OUT) on both [[controller port pinout|controller ports]].
* '''/OE1''' and '''/OE2''' : Controller ports (for controller #1 and #2 respectively). Each enable the output of their respective controller, if present.
* '''R/W''' : Read/write signal, which is used to indicate operations of the same names. Low is write. '''R/W''' stays high/low during the entire read/write cycle.
* '''/NMI''' : Non-maskable interrupt pin. See the 6502 manual and [[CPU interrupts]] for more details.
* '''/IRQ''' : Interrupt pin. See the 6502 manual and [[CPU interrupts]] for more details.
* '''M2''' : Can be considered as a "signals ready" pin. It is a modified version the 6502's φ2 (which roughly corresponds to the CPU input clock φ0) that allows for slower ROMs. CPU cycles begin at the point where '''M2''' goes low.
** In the NTSC 2A03, '''M2''' has a [[Glossary|duty cycle]] of 5/8th, or 350ns/559ns. Equivalently, a CPU read (which happens during the second, high phase of '''M2''') takes 1 and 7/8th PPU cycles. The internal φ2 duty cycle is exactly 1/2 (one half).
** In the PAL 2A07, the duty cycle is not known, but suspected to be 19/32.
** In the PAL 2A07, the duty cycle is not known, but suspected to be 19/32.
* TST (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, extra diagnostic registers to test the sound hardware are enabled from $4018 through $401A, and the joystick ports $4016 and $4017 become open bus.
* '''TST''' : (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, extra diagnostic registers to test the sound hardware are enabled from $4018 through $401A, and the joystick ports $4016 and $4017 become open bus.

Revision as of 07:05, 24 August 2013

Pin out

        .--\/--.
 AD1 <- |01  40| -- +5V
 AD2 <- |02  39| -> OUT0
/RST -> |03  38| -> OUT1
 A00 <- |04  37| -> OUT2
 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| <- TST (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 prefixed by a / (slash) symbol. Every cycle is either a read or a write cycle.
  • CLK : 21.47727 MHz (NTSC) or 26.6017 MHz (PAL) clock input. Internally, this clock is divided by 12 (NTSC 2A03) or 16 (PAL 2A07) to feed the 6502's clock input φ0, which is in turn inverted to form φ1, which is then inverted to form φ2. φ1 is high during the first phase (half-cycle) of each CPU cycle, while φ2 is high during the second phase.
  • AD1 : Audio out pin (both pulse waves).
  • AD2 : Audio out pin (triangle, noise, and DPCM).
  • Axx and Dx : Address and data bus, respectively. Axx holds the target address during the entire read/write cycle. For reads, the value is read from Dx during φ2. For writes, the value appears on Dx during φ2 (and no sooner).
  • OUT0..OUT2 : Output pins used by the controllers ($4016 output latch bits 0-2). These 3 pins are connected to either the NES or Famicom's expansion port, and OUT0 is additionally used as the "strobe" signal (OUT) on both controller ports.
  • /OE1 and /OE2 : Controller ports (for controller #1 and #2 respectively). Each enable the output of their respective controller, if present.
  • R/W : Read/write signal, which is used to indicate operations of the same names. Low is write. R/W stays high/low during the entire read/write cycle.
  • /NMI : Non-maskable interrupt pin. See the 6502 manual and CPU interrupts for more details.
  • /IRQ : Interrupt pin. See the 6502 manual and CPU interrupts for more details.
  • M2 : Can be considered as a "signals ready" pin. It is a modified version the 6502's φ2 (which roughly corresponds to the CPU input clock φ0) that allows for slower ROMs. CPU cycles begin at the point where M2 goes low.
    • In the NTSC 2A03, M2 has a duty cycle of 5/8th, or 350ns/559ns. Equivalently, a CPU read (which happens during the second, high phase of M2) takes 1 and 7/8th PPU cycles. The internal φ2 duty cycle is exactly 1/2 (one half).
    • In the PAL 2A07, the duty cycle is not known, but suspected to be 19/32.
  • TST : (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, extra diagnostic registers to test the sound hardware are enabled from $4018 through $401A, and the joystick ports $4016 and $4017 become open bus.
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