Anomie's SNES Port Doc

@Dreamcast

Published in

SNES

· 8 months ago

Revision: 1132
Date: 2007-04-27 19:31:57 -0400 (Fri, 27 Apr 2007)
<anomie@users.sourceforge.net>

This is a document intended to describe the various hardware ports on the SNES. It will not describe how these ports are used by what may be plugged into them.

In the doc below, "active", "1", "logic-1", and so forth all mean the same thing. Note that "1" does not necessarily correspond to either high or low voltage. (BTW, i could use some help here: if anyone knows whether anything is active-high or active-low, or what the voltages for high and low are for any particular port, please let me know!)

CONTROLLER PORTS

The controller ports of the SNES has 7 pins, laid out something like this:

   _________________ ____________ 
  |                 |            \ 
  | (1) (2) (3) (4) | (5) (6) (7) | 
  |_________________|____________/

The pins are:

+5v (power)
Clock
Latch
Data1
Data2
IOBit
Ground

Latch is written through bit 0 of register $4016. Writing 1 to this bit results in Latch going to whatever state means 'latch' to a joypad.

Clock of Port 1 is connected to the 'read' signal of $4016, in that reading $4016 causes Clock to transition. Data1 and Data2 are then read, and Clock transitions back (at this point, the pad is expected to stick its next bits of data on Data1 and Data2). Clock of Port 2 is connected to $4017.

Data1 and Data2 are read through bits 0 and 1 (respectively) of $4016 and $4017 (for Ports 1 and 2, respectively). Thus, you must read both bits at once, you can't choose to read only Data1 and leave Data2 for later.

IOBit is connected to the I/O Port (which is accessed through registers $4201 and $4213). Port 1's IOBit is connected to bit 6 of the I/O Port, and Port 2's IOBit is connected to bit 7. Note that, since bit 7 of the I/O Port is connected to the PPU Counter Latch, anything plugged into Port 2 may latch the H and V Counters by setting IOBit to 0.

Data1 and Data2 are pulled to logic-0 within the SNES, so reads will return 0 if nothing is plugged in.

CART CONNECTOR

The cart connector has 62 pads, laid out something like this:

                     +--------+ 
     21.477MHz Clock |  1  32 | /WRAM 
              EXPAND |  2  33 | REFRESH 
                 PA6 |  3  34 | PA7 
               /PARD |  4  35 | /PAWR 
                 GND |  5  36 | GND 
F                A11 |  6  37 | A12 
r                A10 |  7  38 | A13 
o                 A9 |  8  39 | A14 
n                 A8 |  9  40 | A15 
t                 A7 | 10  41 | A16 
                  A6 | 11  42 | A17 
o                 A5 | 12  43 | A18 
f                 A4 | 13  44 | A19 
                  A3 | 14  45 | A20 
c                 A2 | 15  46 | A21 
a                 A1 | 16  47 | A22 
r                 A0 | 17  48 | A23 
t               /IRQ | 18  49 | /CART 
                  D0 | 19  50 | D4 
                  D1 | 20  51 | D5 
                  D2 | 21  52 | D6 
                  D3 | 22  53 | D7 
                 /RD | 23  54 | /WR 
   CIC out data (p1) | 24  55 | CIC out data (p2) 
    CIC in data (p7) | 25  56 | CIC in clock (p6) 
              /RESET | 26  57 | CPU_CLOCK 
                 Vcc | 27  58 | Vcc 
                 PA0 | 28  59 | PA1 
                 PA2 | 29  60 | PA3 
                 PA4 | 30  61 | PA5 
    Left Audio Input | 31  62 | Right Audio Input 
                     +--------+

A0-A23 are the Address Bus A lines, /WR and /RD are the associated read and write lines, and /CART and /WRAM are the two auxiliary lines.

PA0-PA7 are the Address Bus B lines, with /PARD and /PAWR the associated read and write lines.

D0-D7 are the data bus lines.

REFRESH is (presumably) the RAM refresh signal sent out each scanline for 40 master cycles.

EXPAND is connected to pad 24 of the expansion port.

/IRQ is connected to the CPU's /IRQ line. This can be read by the cart, or activated by the cart to invoke an IRQ on the CPU.

/RESET is the reset signal, activated by the big reset button on the console. It can also be activated by hardware on the cart, if the system needs to be reset at a hardware level.

CPU_CLOCK is (presumably) the current CPU cycle clock, which is either 6, 8, or 12 master cycles per cycle (3.58MHz, 2.68MHz, or 1.79MHz).

The signals input on Left and Right Audio Inputs are mixed into the APU's output audio.

The CIC pins are connected to the CIC chip, which is used for region lockouts. If the CIC in the console doesn't get the proper handshake over these pads, the reset signal is never released on the PPU2 chip, and so you never get anything on the display.

Many carts connect only to pins 5-27 and 36-58, as the remaining pins are mainly useful only if the cart contains special chips.

EXPANSION PORT

The expansion port has 28 pads, laid out something like this. Note that I have no idea which side of this is towards the front of the SNES, nor whether this is the numbering looking into the console or into the cable.

                     +--------+ 
                 PA0 |  1   2 | PA1 
                 PA2 |  3   4 | PA3 
                 PA4 |  5   6 | PA5 
                 PA6 |  7   8 | PA7 
               /PAWR |  9  10 | /PARD 
                  D0 | 11  12 | D1 
                  D2 | 13  14 | D3 
                  D4 | 15  16 | D5 
                  D6 | 17  18 | D7 
              /RESET | 19  20 | Vcc 
              SMPCLK | 21  22 | DOTCK 
                 GND | 23  24 | EXPAND 
      Mono Audio Out | 25  26 | /IRQ 
       Left Audio In | 27  28 | Right Audio In 
                     +--------+

PA0-PA7 are the Address Bus B lines, with /PARD and /PAWR the associated read and write lines.

D0-D7 are the data bus lines.

/RESET is the reset signal, activated by the big reset button on the console. It can also be activated by hardware on the attached device, if the system needs to be reset at a hardware level.

EXPAND is connected to pad 2 of the cart connector.

/IRQ is connected to the CPU's /IRQ line. This can be read by the attached device, or activated by the attached device to invoke an IRQ on the CPU.

The signals input on Left and Right Audio Inputs are mixed into the APU's output audio. The (mono) audio output is brought back into pin 25.

SMPCLK and DOTCK are not really known. SMPCLK comes from the audio subsystem, reports are that it's about 8.192MHz (i.e. 3 APU master clock cycles per cycle). DOTCK comes from PPU2, and seems to be PPU dot clock at about 5.369 MHz (that's 21.477/4).

MULTI-OUT

The multi-out port has 12 pads, and looks something like this:

  --------^-------- 
 /11  9  7  5  3  1\ 
|                   | 
 \12 10  8  6  4  2/ 
  -----------------

Red analog out
Green analog out
Composite H/V sync out (+11V DC on PAL)
Blue analog out
GND
GND
S-VHS Y (luminance) signal
S-VHS C (chroma) signal
Composite video signal
Vcc
Mid sound (L+R)
Side sound (L-R)

Note: this data from http://www.thepong.com/Sites/Left/Nintendo/SNTech.htm

RF OUT

I know nothing about the output of this port, except that it has a Vcc, a GND, a video signal, and a mono audio signal.

POWER

This one is simple. It's a hollow cylindrical plug. It expects to be supplied with DC 10V, 850mA, with negative in the center and positive on the outside.