Talking to DEC disks controllers with non-DEC hardware(was Re:

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Jun 4 16:55:01 2003

> --- Tony Duell <ard_at_p850ug1.demon.co.uk> wrote:
> > An alternative approach (and one that I'd probably try) would be to use a
> > real RL11 (or similar), a Unibus (or as applicable) RAM card, and a
> > home-made bus master/arbiter that could tall the RL11 to read a sector
> > (using DMA into the RAM card) and could then read out the RAM to the host
> > computer. Doing something like that would let your PC (or whatever) talk
> > to just about any small DEC disk drive using the appropriate Unibus
> > controller.
>
> If you are going to do that, why not use a DEC CPU?

I thought about suggesting that, but the hardware hacker in me wants to
keep it as simple as possible :-). I think I could make a Unibus master
and arbiter in a handful of TTL chips (look at the releveant bits of a
Unibus CPU printset -- it's not that complicated). Using a CPU sounds
like overkill..

There's also the issue that I wanted to keep stuff 'out of the way' I was
thinking it would be useful if the new host could do _anything_ to the
disk controller (that's one good reason to avoidthe BSD device drivers,
actually).

> Why not just use a PDP-11/53 CPU board with local serial and on-board

I don;t have one :-) Anyway, I'm more of a Unibus person...

> If someone wants to design a microcontroller-based Qbus/Unibus register
> thumper from scratch, I'd consider building one. Best to define how
> to talk to it from the outside before getting too far along on the design.

It's a pity that computers with lots of parallel I/O lines are so
uncommon, and the user ports are out of fashion now...

One thing I would _love_ to find is a portable-ish machine which can
write a disk that's readable on a PC, and which has at least 32 parallel
I/O lines, totally user controllable. At the moment I'm using an HP71, a
9114 disk drive, an 82165 GPIO interface and some homebrew hardware
(which is still undergoing hackery). Pity HP never made a real user port
for HPIL....

-tony
Received on Wed Jun 04 2003 - 16:55:01 BST