GPIB state machine info WTD

[Philip Pemberton]

In message <m1EDtUI-000IytC at p850ug1>
          ard at p850ug1.demon.co.uk (Tony Duell) wrote:

> 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.

That's great - thanks. I've dug up a copy of the TMS9914 datasheet, which
seems to be 8 pages of "this register bit does {X}, this one does {Y}".
Either I'm missing part of the datasheet, or it doesn't cover the GPIB states
at all.

> 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

Thanks,
-- 
Phil.                              | Acorn RiscPC600 SA220 64MB+6GB 100baseT
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