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Last updated on Oct-18-2019 Download

FDS and FME7 IRQs - Same, but Different Regs/Addresses?

FDS and FME7 IRQs - Same, but Different Regs/Addresses?
by on (#78437)
I had to post the following because it may be possible to port a FDS game with fewer modifications to FME7, as well as MMC5 as an alternative.

One such thing is the IRQs, IRQs is much easier on FME7-compatibles because of it being based off the fact that sunsoft developed on FDS software.
(see LostLevels.Org Forums - Sunsoft Dev Disks thread)

In the wiki, both FME7 and FDS:

$4020-$4021 is the same as $0e-$0f, more likely derived from FDS technology (CPU-based IRQ)

$0c must be $81 (%10000001) as opposed to $02 in FDS (%00000010) to enable IRQs, but FDS uses it also for Disk transfer.

My own and some from the wiki:

FDS IRQs can be read to acknowlage itself, But you must do something else with FME7,

This may not be the case, but I am guessing disabling it via #$00 in both $0e-$0f if resetting and #$00 in $0c.

Anyone who will make an update to both sections explaining similatiries inbetween the mappers will be appreciated

OFF TOPIC EDIT: Also of note is $6000 is swichable ROM as well as RAM, and FDS games use $6000 also, Why not make a use of that when porting it to this mapper?