The CPC+/GX4000 has a female 2x18 pin cart-edge connector for cartridges.
In the schematics, the pins are numbered A1..A18 and B1..B18. However, the text layer on the cartridge PCBs typically uses a different numbering: 1..36 (with even numbers on the solder side of the cartridge) (and with numbers ordered in opposite direction):
component side solder side 1 B18 VCC 2 A18 VCC ________________________ 3 B17 CLK4 4 A17 CA18/LK2 (B18) 1 | | 35 (B1) 5 B16 CA16 6 A16 CA17/LK4 |_ ------------------ _| 7 B15 CA15/LK6 8 A15 CA14 (A18) 2 |____________________| 36 (A1) 9 B14 A12 10 A14 A13 11 B13 A7 12 A13 A8 13 B12 A6 14 A12 A9 15 B11 A5 16 A11 A11 17 B10 A4 18 A10 A3 19 B9 A10 20 A9 A2 21 B8 /CE 22 A8 A1 23 B7 D7 24 A7 A0 25 B6 D6 26 A6 D0 27 B5 D5 28 A5 D1 29 B4 D4 30 A4 D2 31 B3 D3 32 A3 SIN 33 B2 CCLR 34 A2 GND 35 B1 GND 36 A1 GND
- The SIN,CCLR,CLK4 pins are special signals for the ACID chip. Cartridges won't work without ACID.
- Note: Arnold V specs say that "ROM CARTRIDGE: 2 pcs 2 x 9 way 2.5mm pitch sockets." This seems to be nonsense (or might refer to an internal connector on the mainboard). The external cartridge connector has 2x18 pins - not 2x2x9 pins.