Talk:INES Mapper 099: Difference between revisions
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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. —[[User:Lidnariq|Lidnariq]] ([[User talk:Lidnariq|talk]]) 16:15, 31 October 2013 (MDT) | 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. —[[User:Lidnariq|Lidnariq]] ([[User talk:Lidnariq|talk]]) 16:15, 31 October 2013 (MDT) | ||
: Half of the 7474 can be configured to [http://forums.nesdev.org/viewtopic.php?p=125760#p125760 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.) —[[User:Lidnariq|Lidnariq]] ([[User talk:Lidnariq|talk]]) 23:25, 3 May 2014 (MDT) | |||
Revision as of 05:25, 4 May 2014
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)
