Serial interfaces (was Re: Any former Psion 5 owners out there?)

[Tony Duell]

> 
> On 7/27/10, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> > Goin back ot the very early Unibus devices, there were 3 cards -- the
> > device controlelr itself, an M105 address selector (which had jumpers to
> > set the device address) and an M782/M7820/M7821 Interrupt card which had
> > the jumpers to set the vector.
> 
> Good point.  I had forgotten about those - all of my comments apply to
> SPCs (Small Peripheral Controllers), not backplane-sized devices
> (there were a few SPCs even in the earliest days, like the LP11 I
> mentioned).
> 

Actually, the original SPCs were 3 boards. A dual-height board containing 
the specific device control/interface circuity that went in connectors C 
and D of the SPC slot, an M105 address selector module in connector E and a 
M782 (or M7820, M7821) interrupt logic module in connector F. That's why 
there are connections betweeen the various connectos on the SPC slot. 

I hae a DR11-A that's like that, and I think I have a KL11 (current loop 
only console port) done that way too. And possibly some others.

Even when everything went on one quad-height SPC card, some devices still 
consisted of 3 independant circuits on that card, connected via the 
backplane connecotrs only, In other words there would be an address 
selector circuit on the quad card conencted to connector E only. It would 
output the approrpiate eanble signals on fingers of connector E, they 
would then be routed to connector C/D via the backplane and thus to the 
device logic. My PC11 is built that way.

I also have some 3rd party dual height cards that combine the functions 
of the address sekector and interrupt logic and which go in connectors 
E?F, along with a dual-height SPC card in C/D

-tony