CDOS seems to be hanging waiting for the interrupt (or the DRQ) from the 1793

The INTRQ is set when the 1793 is done, and is cleared by a read from the status register or a write to the command register.

A spurious read from the status register or write to the command register might cause the symptoms...

we have seen this problem during read-only transactions, so we know it must be at least partiall on the read side of things.

1793 Read Enable is generated by the undocumented PAL at IC37.

IC37  has the following inputs:

  NOT (-sINP)
  delayed NOT (-sOUT)
  A0 - A6
  -S input (-select?) = -[  -(-A7 AND -(-pHLDA)) AND  (-(-sINP) OR -(-sOUT)) ]

so a glitch on this -S line would do it... -SINP glitch or -SOUT glitch... 


XMODEM note:

terminal mode: let the user specify the exit character, default to, for example, %