74xx161-based boards were used in many games. Being based on an off-the-shelf general purpose 4-bit counter, these boards have less functionality compared to ASIC mappers specifically designed to take advantage of the Famicom's specifications. When converting such a board to flash memory, certain problems will still exist:
Devices that support A0-A10 command addresses are supported (e.g. AM29B040B). Unfortunately this type of board is unable to allocate A0-A14 command addresses.
So far, HVC-UNROM-10 and HVC-UOROM-01 have been successfully tested. Other 74xx161-based boards not referenced in this document might not comply with the following instructions.
The unreferenced wires will depend on hardware design. However there shouldn't be any problem with these referenced wires.
Add a 74xx00. Using the same 'xx' family of 74xx161 devices that already exists on the board is recommended.
74xx00 +-v--+ CPU R/W -+-|1 14|--- +5V | | | +-|2 13|-+- CPU /ROMCS | | | PRG /OE -+-|3 12|-+ | | | +-|4 11|-+ | | | | +-|5 10|-+ | | NC |6 9|--- CPU PHI2 | | GND ---|7 8|--- 74xx161 CK +----+
Since the MaskROM of a UNROM board has only 28 pins, modifying this type of board is not recommended. It may be possible to replace the MaskROM with a 32-pin flash memory chip, but the chip will stick out on the board as a side effect. So if you're wanting to keep a cartridge casing intact, a game containing a UOROM board would be a better choice. In addition, hardwiring any connections would be much more stable.
1:A17 32:+5V 2:*1 31:+5V 30:+5V 24:A16 22:CPU /ROMCS
1:A18 = mask ROM 1pin, UxROM Program A17 (optional, *2) 2:A16 = mask ROM 24pin, UxROM Program A16 31:/WE = cartridge 14pin, CPU R/W 30:A17 = mask ROM 1pin, +5V (optional) 24:/OE = 74xx00 3pin 22:/CS = cartridge 44pin, CPU /ROMCS (unchanged wiring)