Legacy apps in Windows/OS X was Re: Old MS-DOS & Win Software

Allison ajp166 at bellatlantic.net
Thu Dec 8 16:14:38 CST 2005


>
>Subject: Re: Legacy apps in Windows/OS X was Re: Old MS-DOS & Win Software
>   From: Jim Leonard <trixter at oldskool.org>
>   Date: Thu, 08 Dec 2005 15:55:58 -0600
>     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>
>Chuck Guzis wrote:
>> codes.  Inspection of the 808x instruction set can be very illuminiating,
>> particularly when it comes to arcana like which instructions modify (and
>> how) the half-carry flag, for example.
>
>The "half-carry flag"?  Huh?

You lived a shelterd life.

8080/8085 have a flag that is set when ther eis a carry from the low 4 
bits to the upper as part of the DAA (Decimal Adjust Accumulator).  Not
only is it mostly undocumented therre are a bunch of instructions like
Jumps that work with it also undocumented.   While I've never deleved 
deeper than I had to with 8086/88 I'd bet it exits there and and with 
a few more permutations added. It's not unique to Intel!


Allison



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