HuC1 is an MBC developed by Hudson Soft. It implements ROM and RAM banking, and also provides infrared communication. Despite many sources on the internet claiming that HuC1 is “similar to MBC1”, it actually differs from MBC1 significantly.
|$0000–1FFF||RAM/IR select (when writing only)|
|$2000–3FFF||ROM bank select (when writing only)|
|$4000–5FFF||RAM bank select (when writing only)|
|$A000–BFFF||Cart RAM or IR register|
Most MBCs can disable the cartridge RAM to prevent accidental writes. HuC1 doesn’t do this. Instead, this register swtiches the $A000–BFFF region between “RAM mode” and “IR mode” (described below). Write $0E to switch to IR mode, or anything else to switch to RAM mode.
Some HuC1 games still write $0A and $00 to this region as if it would enable/disable cart RAM.
HuC1 can accept a bank number of at least 6 bits here.
HuC1 can accept a bank number of at least 2 bits here.
Writes to this region seem to have no effect. Even so, some games do write to this region, as if it had the same effect as on MBC1. You may safely ignore these writes.
When in “IR mode” (wrote $0E to $0000), the IR register is visible here. Write to this region to control the IR transmitter. $01 turns it on, $00 turns it off. Read from this region to see either $C1 (saw light) or $C0 (did not see light).
When in “RAM mode” (wrote something other than $0E to $0000) this region behaves like normal cart RAM.