9464C-0036 BIOS mask ROM (ColecoVision U2) pinout

DIP-28. OS-7 BIOS, $0000-$1FFF

The stock BIOS ROM at U2. It is not a 2764 pinout: pin 2 is NC, pin 20 is A11, pin 23 is A12 and pin 22 is the enable /EP, where a 2764 has A12, /CE and A11 on 2, 20 and 23. Pins 1, 26, 27 and 28 are all tied to +5 V on the board (26 is VCC on this part, 28 on a 2764). To fit a 2764 EPROM, sever the two solder traces by U2 and add jumpers WJ4 (pin 20 to the select) and WJ5 (pin 23 to A11), as the schematic note says. /EP comes from U5 (74LS138) output O0, the $0000-$1FFF select.

Open the interactive 9464C pinout

Pins

Pin	Name	Type	Signal
1	NC	nc	No connection on the 9464C; tied to +5 V on the board (VPP on a 2764).
2	NC	nc	No connection on the 9464C. A 2764 has A12 here; the board links this pad to A12 for the EPROM conversion.
3	A7	addr	Address bit 7.
4	A6	addr	Address bit 6.
5	A5	addr	Address bit 5.
6	A4	addr	Address bit 4.
7	A3	addr	Address bit 3.
8	A2	addr	Address bit 2.
9	A1	addr	Address bit 1.
10	A0	addr	Address bit 0.
11	D0	data	Data bit 0.
12	D1	data	Data bit 1.
13	D2	data	Data bit 2.
14	VSS	ground	0 V.
15	D3	data	Data bit 3.
16	D4	data	Data bit 4.
17	D5	data	Data bit 5.
18	D6	data	Data bit 6.
19	D7	data	Data bit 7.
20	A11	addr	Address bit 11 (through a solder trace that the EPROM conversion severs; a 2764 has /CE here).
21	A10	addr	Address bit 10.
22	/EP	ctrl	Enable, active LOW, from U5 (74LS138) O0, the $0000-$1FFF select.
23	A12	addr	Address bit 12 (a 2764 has A11 here; jumper WJ5 moves A11 to this pin for an EPROM).
24	A9	addr	Address bit 9.
25	A8	addr	Address bit 8.
26	VCC	power	+5 V supply on the 9464C (NC on a 2764).
27	NC	nc	No connection; tied to +5 V on the board (/PGM on a 2764).
28	NC	nc	No connection on the 9464C; tied to +5 V on the board (VCC on a 2764).

Fitted in

ColecoVision

Sources

ColecoVision schematic, KiCad redraw Rev J (colecovisionadam.com), sheet 9: U2 9464C-0036 pin numbers, solder traces and jumpers WJ4/WJ5 (EEPROM note)