Talk:INES Mapper 099

Minimal discrete logic clone

A 74138, selecting on M2, A14, A4, and A1 high; R/W and A0 low, and a 7474 (or any larger latch). Maps the write-only register at every address [4-7C-F].[13579BDF][26AE]. Conflicts on writes to $4012 and DualSystem games that communicate using RAM. Using a 74161 or any other latch with an additional active-low enable would remove the conflict with the DualSystem RAM; however, there's no obvious place to get an extra active-high enable to prevent the conflict with $4012. —Lidnariq (talk) 16:15, 31 October 2013 (MDT)

Half of the 7474 can be configured to act as an inverter. In this case, instead of requiring A0 low, we could instead require A2 high, mapping the register at [4-7C-F].[13579BDF][67EF]. Now it conflicts with writes to $4017, but few games will write to that register more than once. (It still conflicts with writes to the RAM at $6xxx.) —Lidnariq (talk) 23:25, 3 May 2014 (MDT)