On the 8080 there are many instructions with parallel forms. Three of these are
JP, which all have conditional and immediate forms.
Note: I am using Z80 terminology because that is what I am familiar with.
<cond> represents a flag/value combination:
0 - NZ (Z=0, Non Zero) 1 - Z (Z=1, Zero) 2 - NC (C=0, Non Carry) 3 - C (C=1, Carry) 4 - PO (V=0, Parity Odd / non oVerflow) 5 - PE (V=1, Parity Even / oVerflow) 6 - P (S=0, Sign Plus) 7 - M (S=1, Sign Minus)
The immediate forms are:
All of the
JP instructions take the next two bytes as the 16-bit address to go to, but that is irrelevant to my question.
The 8080 did not define instruction
313, which was later used by the Z80 to expand the instruction set. Why did the designers of the 8080 not use
313 for JumP immediate, and leave
303 undefined instead?