Stupid question that's been annoying me - test-drb@ccmp.vtda.org

30 Sep 2001

On Sep 30, 13:54, Cameron Kaiser wrote:
...
  > Maybe part of the confusion arises because many
processors (including the
...
  > 8080) complement the carry flag at the end of a
subtraction, so that it can
...
   be used
directly as a "borrow" flag in multibyte subtractions.  Others
 (like the 6502) don't do that. 
 I'm not sure what you mean by this, but on my C128,
 1300 ad 01 04  lda $0401
 1303 38                sec 
That's my point: you have to SEC first.  You would clear it on most other
processors.  Also, after a subtraction, the 6502 sets the carry to 0 if a
borrow was necessary, or to 1 if not; a 6800, 8080, or Z80 does the
opposite.
--
Pete                                            Peter Turnbull
                                                Network Manager
                                                University of York