Hi!
Several years age, I have made a project based on Z80 processor and I don't know what happens to the 1 of 3 Z80 processor I have. But when I run a program on it certain perticular instruction doesnot gave response which it should give. I think it was some mathmatical instruction and it was hard to found out about it, but luckly I find it out. It also proved by inserting the other 2 processors in the first one with same program on which the first one fails. Here I should tell you a very interesting fact that at that time I haven't have a personal PC and programmer. So I used to write program on a rough copy and then compile it to machine code by hand and the copy it to EPROM by a 74ls373 latch based hand made programmer.