Front Panels - Thoughts

[Brent Hilpert]

On 2015-Nov-01, at 12:27 AM, rod wrote:
> On 31/10/15 21:36, tony duell wrote:
>>> Hi Tony
>>>             I seem to remember, certainly in OEM land there were dev.
>>> systems with front panels and production systems without.
>>> In other words  the front panel was option and could be fitted.
>> Sure. The PDP8/f and PDP8/m are the well-known example. Many of the
>> Philips P800s had optional full panels too (fortunately the ones I own
>> do have the full panels). And there must be many more
>> 
>> But I still claim it is difficult to add a panel to a machine that was never
>> designed to have one. In the case of machines with optional full
>> frontpanels the machine was designed to take a frontpanel and either
>> to also run without it or there was some minimal panel (boot/reset/not
>> much else) that provided enough logic that the processor didn't realise
>> it didn't have the full panel (if you see what I mean).
>> 
>> -tony

> Yes much as I thought. What about S100 systems?
> Many did have lamps and switches but I can think of a couple that didn't .
> Northstar Horizon for one and Cromenco also.

The other way round I think, the Altair and IMSAI were the only S100 machines I recall OTTOMH which had blinkenlight panels.
The vast majority of them didn't. Northstar & Cromemco as you say, Compu-Pro, Vector-Graphic, Processor Tech SOL, Poly 88, etc. : no blinken.

One problem with a front panel on an S100 machine - or any microprocessor-based machine - is getting access to the program counter so you can tell it to start running at some arbitrary address. The Altair/IMSAI panels resolved this with a hack, jamming a jump instruction into the processor data lines (not the S100 bus data lines) via a special connector to a special processor card.

In general, even if you can bus master to put stuff into memory, front panel functionality is pretty limited if you don't have control ever execution.