[A83] Re: Getkey loop


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[A83] Re: Getkey loop




As a note, it is a GREAT idea to go over to www.zilog.com and check out the 
actual manual for the Z80 processor. Once you learn the notation they use, 
which isn't too esoteric, it will become a valuable learning tool. It has the 
(almost) complete instruction set, with opcodes, flags set, clock cycles, and 
explanations + more.

The CP instruction can perform two simulated subtraction operations:

A(register) - K(constant)
or
A(register) - G(register), where G is an 8-bit register such as B, C, D, or E

The flags are set as follows:
NC, or there is NO CARRY if A - X >= 0.
*In this case, X would be equal to or less than A.

C, or there is a CARRY if A - X < 0.
*In this case, X would be greater than A.

NZ, or the result is NOT ZERO if A does not equal X

Z, or ZERO, if A = X

Essentially, the CP operation is the same as the SUB A,X operation, but it 
doesn't return the result in A.

Hope this helps,
Tom

p.s. This was all off the top of my head, so if I may have made a minor error 
somewhere...



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