MC-ACC pinout

MC-ACC chip: (40-pin 0.6" DIP)

               .--\/--.
        GND ?? |01  40| -- 5V
(r) PRG A16 <- |02  39| ?? PRG A18??
(r) PRG A15 <- |03  38| -> PRG A17 (r)
(n) CPU A14 -> |04  37| -> PRG A14 (r)
(n) CPU A13 -> |05  36| -> PRG A13 (r)
        n/c ?? |06  35| <- CPU R/W (n)
        n/c ?? |07  34| <- /ROMSEL (n)
        n/c ?? |08  33| -> PRG /OE (r)
(nr) CPU A0 -> |09  32| <- CPU D7 (nr)
(nr) CPU D0 -> |10  31| <- CPU D6 (nr)
(nr) CPU D1 -> |11  30| <- CPU D5 (nr)
(nr) CPU D2 -> |12  29| <- CPU D4 (nr)
(r) CHR A16 <- |13  28| <- CPU D3 (nr)
(r) CHR A15 <- |14  27| -> CIRAM A10 (n)
(r) CHR A14 <- |15  26| -> CHR A17 (r)
(r) CHR A13 <- |16  25| -> /IRQ (n)
(r) CHR A12 <- |17  24| <- PPU A12 (n)
(r) CHR A11 <- |18  23| <- PPU A11 (n)
(r) CHR A10 <- |19  22| <- PPU A10 (n)
        GND -- |20  21| <- M2 (n)
               '------'

39: speculative
24: on the 55741 PCB, buffered via several gates of a 74'08 to add a few tens of ns extra delay, presumably for the IRQ

Source: https://forums.nesdev.org/viewtopic.php?p=16795#p16795