Date   : Wed, 20 Jul 1994 20:46:06
From   : JAMES WARD <J.Ward@...>
Subject: Progress Report and some questions...

1. What is the V flag for? Is it user-definable and that's it?
   I believe this is the overflow flag.
   If I am not mistaken it might even correspond to the same flag-
   bit position as the PC uses in LAHF.

2. What does BIT do?
   Tests bits by performing a logical AND

3. Why have a direction flag, seeing as no operations I can see are
direcitonal?
   Oh, are we talking about 80x86 here then?
   If we are... then the direction flag is used for REP prefixed
   operations (string operations) such as REP MOVSB (which transfers
   a string of bytes, incrementing SI and DI (the pointers) as it
   goes.  The direction flag controls whether it goes up or down.

4. (PC question) does, for example, mov AX,[DS:SI] use up fewer clock
cycles than mov AX,[DS:SI]+1? I've looked in my TASM manual but I'm
buggered if I can follow it...
   I shouldn't worry about subtleties like that...

5. What do PHP/PLP do?
   Pushes and pulls the processor status flags.
   Make sure the bits are in the right order...

6. What does RTI do?
   Return from Interrupt.

Hey, if I made any mistakes here.... go ahead and flame me, I
probably deserve it :-)
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( E-Mail:  j.ward@...                                        )
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