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.