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mg_notes:iie_card:weird_stuff [2017/08/07 22:25] M.G. Slot scan/select description. |
mg_notes:iie_card:weird_stuff [2018/12/21 17:53] M.G. [Slot Scan Scam] |
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- | $02 is a two-byte NOP on the 65C02. Interestingly enough, when the processor on the Card executes the sequence $02 $01, it produces the configured beep sound. | + | $02 is a two-byte NOP on the 65C02 (if it was an '802 or '816 it'd be a COP). Interestingly enough, when the processor on the Card executes the sequence $02 $01, it produces the configured beep sound. |
Try this in the monitor: | Try this in the monitor: | ||
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The $02 $03 sequence behaves as if CMP #$C0 or CMP #$Cn-1 has been executed and if it has, displays "UNABLE TO BOOT FROM STARTUP SLOT" in the center of the screen in a similar manner to the copyright message. The message is not in Apple II memory. It returns with the flags set as executing the CMP instruction would have. | The $02 $03 sequence behaves as if CMP #$C0 or CMP #$Cn-1 has been executed and if it has, displays "UNABLE TO BOOT FROM STARTUP SLOT" in the center of the screen in a similar manner to the copyright message. The message is not in Apple II memory. It returns with the flags set as executing the CMP instruction would have. | ||
+ | My ''iie.card'' [[https://github.com/mgcaret/davex-mg-utils/blob/master/iie.card.s|utility]] for Davex can exploit this to determine which slot is configured for startup via the [[https://github.com/mgcaret/davex-mg-utils/blob/master/iie.card.s#L118|dispslot routine]]. |