10 Sep
2005
10 Sep
'05
8:43 p.m.
I also
designed a GPIB listener state machine in a GAL. Again I should
have the equations somewhere...
I think I saw that somewhere.. A PET GPIB to Centronics adapter, right? 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.
Well, if it only just works on a 2MHz 6502, it's a sure bet it'll probably
fail at 8MHz.
I only wanted the IEEE488 part of the interface anyway - the CPU interfacing
gubbins2