The following code *does* set the Auxilary Carry (AC):

MOV A,#10h
SUBB A,#08h

After executing the SUBB instruction, AC should be set. If JSIM doesn't set the AC bit with the above code, that'd be a bug in JSIM.

If Timer 1 (TH1/TL1) is in mode 3 (split timer), it stops. In any other mode, it counts normally--but it will no longer provoke interrupts or set the TF1 overflow bit. You can use it to establish baud rate, however.

Craig Steiner