GPIB state machine info WTD

I built a GPIB interface from TTL years ago, from what I remember it was quite simple. Let me see if I can find schematics if you don't get more useful replies. I also designed a GPIB listener state machine in a GAL. Again I should have the equations somewhere... Be _very_ careful if you use designs intended for the PET. The PET was very forgiving in the timing of the peripherals. I have a commercial PET RS232 interface that contains a UART chip, RS232 buffers, a few TTL chips as SR latches to hold the talk and listen states, an EPROM as the code converter (PERSCI-ASCII) and talk/listen address detector) and another EPROM as the handshake control logic. Due to the fact there are no latches in the latter section, the timing goes all over the place. It works on the PET, it doesn't work on any HP machine I've tried it with. -tony