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There are several bugs in the NMOS version of the CPU. One of them is with regard to the buggy IFF2->parity flag performance in the LD A,I and LD A,R instructions. An error can occur when an INTACK runs near these instructions, the parity flag will be showing 0 when it should have been 1. We are not sure but this bug concerns the CMOS Z80 too. A Zilog app. note is around somewhere talking about this.
Information source
This document page is based on combined information from articles written by :
Sean Young, syoung@cs.vu.nl
Mark Rison, mrison@acorn.co.uk
Marat Fayzullin, fms@freeflight.com
The original PDF contains more details, click on link to read / download, z80-documented-v0.91.pdf.