On Mon, 8 Jul 2002, Paul Slocum wrote:
> 1) What is the difference between overflow and carry?
For addition, the carry bit is set when the result is to large to fit
in a byte. For subtration, the carry (borrow) bit is set when you
try to subract a number from a smaller number.
The overflow bit works the same way, but for signed integers.
I.E. the largest value you can have is 127, and the smallest you can
have is -128.
Try running a couple of tests with ADC and SBC to see how the differences
work. The overflow flag is also set by the BIT instruction, and the stack
operators too.
> 2) What are some common situations where EOR is useful?
If you want to flip a bit without knowledge of it's current value,
you can EOR it with 1. EOR is also used to test for equality.
For example:
; testing if value is $45
EOR #45 ; unlike BIT, this changes the accumulator value
BNE Not_45
Is_45 ......
......
Not_45 ......
Exclusive OR is also used in most LFSR (pseudo-random number generator)
implementations.
-Chris
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