The DOS/AMSDOS rom has been patched in the following way:
* At offset &56D instead of:
CALL &c976
there is:
C1 18 11
....
* At offset &763 instead of:
CALL &c976
there is:
SCF
RET
* At offset &1c00 the following code has been added (on CPC this is filled with 0x0ff):