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LC //e Card - Weird Stuff

Weird Beep

The //e Card is able to replace the standard Apple II beep with a Macintosh sound. The means by which this is accomplished is quite interesting.

The routine at $fbdd (BELL1) is

  .org $fbdd
  ; this code replaces the .1 second delay
  .byte $02  ; two byte NOP in 65C02
  .byte $01  ; should be ignored by CPU
  ; remaining code matches the original //e code and calling $fbe2
  ; will produce a beep, at the wrong pitch if the card is in fast mode.

$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.

Try this in the monitor:

*300:02 01 02 01 02 01 60

Three beep sounds!

So this must be part of the magic that interfaces the card to the host Macintosh. How very very interesting.

Other Weird Instructions

The preceding find led me to search through the monitor ROM to look for other unusual instruction sequences.

Here is what I found:

In Routine Address Code Function
RESET $FAB4 $02 $02 ?
RESET $FAC0 $02 $03 ?
APPLEII $FB63 $02 $04 Display copyright message on screen, disappears if screen scrolls.
BELL1 $FBDD $02 $01 Play system bell sound.
GETLN1 $FD78 $02 $06 Key translation called right after rdchar. Converts A reg from DELETE to .