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mg_notes:iie_card:weird_stuff [2017/08/06 03:22] M.G. [Other Weird Instructions] |
mg_notes:iie_card:weird_stuff [2017/08/07 22:25] M.G. Slot scan/select description. |
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| ^ In Routine ^ Address ^ Code ^ Function ^ | ^ In Routine ^ Address ^ Code ^ Function ^ | ||
| - | | RESET | $FAB4 | $02 $02 | ? | | + | | PWRUP | $FAB4 | $02 $02 | Loads A reg with $Cn+1 where n = startup slot or $C8 if scan. | |
| - | | RESET | $FAC0 | $02 $03 | ? | | + | | PWRUP | $FAC0 | $02 $03 | Displays "UNABLE TO BOOT FROM STARTUP SLOT" if A reg = $Cn-1 where n = startup slot or $c0 if scan. Disappears if screen scrolls. | |
| | APPLEII | $FB63 | $02 $04 | Display copyright message on screen, disappears if screen scrolls. | | | APPLEII | $FB63 | $02 $04 | Display copyright message on screen, disappears if screen scrolls. | | ||
| | BELL1 | $FBDD | $02 $01 | Play system bell sound. | | | BELL1 | $FBDD | $02 $01 | Play system bell sound. | | ||
| - | | GETLN1 | $FD78 | $02 $06 | Key translation called right after rdchar. Converts A reg from <key>DELETE</key> to <key><-</key>. | | + | | GETLN1 | $FD78 | $02 $06 | Key translation called right after rdchar. If A reg has <key>DELETE</key>, converts it to <key><-</key>. | |
| + | | | | $02 $05 | Not found in firmware, yet, but presumably this exists. | | ||
| ==== The Key Translation and the A register ==== | ==== The Key Translation and the A register ==== | ||
| Line 59: | Line 60: | ||
| </code> | </code> | ||
| - | FD35 is the RDCHAR routine, FDDA is the print byte routine. This routine reads a keypress and outputs its hex code. Run it a few times to convince yourself there is no funny business. Run it a final time and press the delete key. | + | FD35 is the RDCHAR routine, FDDA is the print byte routine. This routine reads a keypress and outputs its hex code. Run it a few times to convince yourself there is no funny business. Run it a final time and press <key>DELETE</key>. |
| <code> | <code> | ||
| Line 67: | Line 68: | ||
| </code> | </code> | ||
| - | Now want to see something interesting? Change the NOPs to $02 $06 and run it again. Press delete. | + | FF is exactly what we expect to see with the Apple II delete key. |
| + | |||
| + | Now want to see something interesting? Change the NOPs to $02 $06 and run it again. Try a few keys, then try it with <key>DELETE</key>. | ||
| <code> | <code> | ||
| Line 76: | Line 79: | ||
| </code> | </code> | ||
| - | That's some serious magic. | + | 88 is the code for the left arrow key. That's some serious magic, and in two bytes the Card converts <key>DELETE</key> to <key><-</key>. |
| + | |||
| + | ==== The Two-Byte Copyright ==== | ||
| + | |||
| + | Try this sequence of instructions: | ||
| + | |||
| + | <code> | ||
| + | ]HOME | ||
| + | ]CALL -151 | ||
| + | *300:02 04 60 | ||
| + | *300G | ||
| + | </code> | ||
| + | |||
| + | Hit the left arrow a bunch of times until the display scrolls. **POOF!** | ||
| + | |||
| + | ==== Slot Scan Scam ==== | ||
| + | |||
| + | The %%//%%e Card lets the user pick the startup slot in the control panel or "Scan" which is the behavior of a standard %%//%%e. | ||
| + | |||
| + | This is implemented by the sequences $02 $02 which replaces the LDA #$C8 at the start of the slot scan loop, and $02 $03 which replaces the CMP #$C0 instruction that decides loop termination. | ||
| + | |||
| + | The $02 $02 sequence loads the accumulator with $C8 if scan is selected, or $Cn+1 if a specific slot is selected. | ||
| + | |||
| + | <code> | ||
| + | *300:02 02 4C DA FD | ||
| + | *300G | ||
| + | C8 (if scan or slot 7 selected, "Cx" if another slot is selected) | ||
| + | * | ||
| + | </code> | ||
| + | |||
| + | 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. | ||