Sunsoft 4 pinout

Sunsoft 4: 40-pin 0.6" PDIP

             .---\/---.
       M2 -> | 01  40 | -- +5V
  /ROMSEL -> | 02  39 | <- R/W
  CPU A14 -> | 03  38 | <- CPU D6
  CPU A13 -> | 04  37 | <- CPU D5
  CPU A12 -> | 05  36 | <- CPU D4
 PPU /A13 -> | 06  35 | <- CPU D3
  PPU A12 -> | 07  34 | <- CPU D2
  PPU A11 -> | 08  33 | <- CPU D1
  PPU A10 -> | 09  32 | <- CPU D0
     ?GND -> | 10  31 | <- OR A (PPU /RD)
  PRG /CE <- | 11  30 | <- OR B (SS4 /CHRSEL)
  CHR A17 <- | 12  29 | -> OR Y (CHR /CS)
  CHR A16 <- | 13  28 | -> CIRAM /CS
  CHR A15 <- | 14  27 | -> SS4 /CHRSEL
  CHR A14 <- | 15  26 | -> WRAM /CE
  CHR A13 <- | 16  25 | -> PRG A14
  CHR A12 <- | 17  24 | -> PRG A15
  CHR A11 <- | 18  23 | -> PRG A16
  CHR A10 <- | 19  22 | -> PRG A17
      GND -- | 20  21 | -> WRAM +CE
             `--------'

10 probably actually some control, not a supply pin
19 also connects to CIRAM A10
29,30,31 actually just an OR gate; for use with a 28-pin 128KB CHR-ROM

Reference: Naruko's notes