alt Hacker NewsThe article claims: > The Z80 is fully binary compatible with the 8080 instruction set.
It wasn't in regards to the flag register. The parity flag behaved differently for some ops.
And of course it would be possible to write an 8080 program that used undefined ops that would execute in some random way (often just duplicating an existing instruction) while the Z80 repurposed that opcode for something new.
But "undefined ops" are not part of the "8080 instruction set"; supporting those would be "binary compatible with the 8080 silicon".
The parity flag is a breaker though; "binary compatible for code only relying on the 8080 instruction set, other than values of the parity flag".