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Internals.md

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CCGMS Internals

Here are some details that will help with development.

Memory Map

  • Low
Range Use
$0380-$03FF UP9600 byte reversal table
$0400-$05FF Punter buffers (screen RAM!)
  • High
Range Use Alt use
$C800-$CAFF XMODEM buffer
$CB00-$CBFF Multi-Punter buffer XMODEM buffer (cont.)
$CC00-$CCFF buffer to save return text from dialing CRC table lo
$CD00-$CDFF Punter temporary vars CRC table hi
$CE00-$CEFF RS-232 input buffer
$CF00-$CFFF text input buffer
  • 40 column mode:
Range Use
$D000-$DFFF unused
$E000-$FFCF screen snapshots
  • 80 column mode:
Range Use
$D000-$D3FF 4x8 charset
$D400-$D7E7 40x25 "screen memory" holding the colors
$D800-$DFCF logical 80x25 screen RAM
$E000-$FE3F bitmap

Banking

CCGMS runs with $01 = $37. Whenever you want to turn off the KERNAL ROM, you need to store #$34 in $01. This is effectively the same as #$30, but allows the timing-critical UP9600 code to switch I/O on and off with inc $01 and dec $01.