2600/7800 bankswitch question...

[Nukey Shay]

I gather that a JMP instruction which exists at $xFF6-8 would automatically cause a bankswitch to the 3rd bank in a -F6 16k game (because $xFF8 is the last hotspot address hit by the P.C.)...and that a JMP that exists at $xFF9-B similarly would cause a bankswitch to the last bank (because of $xFF9). At least that is how it looks to work in Z26...but does this operate differently with a 7800 console (vs. a 2600)?

BTW all 4 banks would probably need identical data at those addresses too, correct (just in case of lag)?

[+batari]

I gather that a JMP instruction which exists at $xFF6-8 would automatically cause a bankswitch to the 3rd bank in a -F6 16k game (because $xFF8 is the last hotspot address hit by the P.C.)...and that a JMP that exists at $xFF9-B similarly would cause a bankswitch to the last bank (because of $xFF9). At least that is how it looks to work in Z26...but does this operate differently with a 7800 console (vs. a 2600)?

BTW all 4 banks would probably need identical data at those addresses too, correct (just in case of lag)?

What will happen in the first case depends on the bankswitching hardware. Level-triggered hardware should act as above, but edge-triggered hardware will ignore the subsequent hotspots (though I may have that backwards.)

 

However, starting the code at $xFF9 should have the desired effect on either hardware, as long as you don't read while the upper address line is changing (or there isn't any consequence if you do.)