Altair 8800C without front panel

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Altair 8800C without front panel

Postby TheoAU » July 24th, 2022, 1:12 am

Now that I've successfully built the CPU reproduction, I plan on acquiring and building the 9 slot backplane with power supplies.

Can I have a working system without a front panel by populating the backplane with CPU, FDC+ and using the jump on start feature of the 882SIOJP to boot into the monitor?
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Re: Altair 8800C without front panel

Postby AltairClone » July 24th, 2022, 10:49 pm

That should work as long as your 2SIOJP is new enough to have some of the front panel replacement features. This includes MWRITE generation, sense switches, and pull-up or two for a couple of bus signals driven from the front panel board.

Mike
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Re: Altair 8800C without front panel

Postby TheoAU » July 25th, 2022, 6:32 am

AltairClone wrote:That should work as long as your 2SIOJP is new enough to have some of the front panel replacement features. This includes MWRITE generation, sense switches, and pull-up or two for a couple of bus signals driven from the front panel board.

Mike


Thanks Mike. I have a revision C 88-2SIOJP. My manual is dated 16 Aug 2016. It doesn't look like it generates the MWRITE. There's a reference to SMWRITE on page 15:

"The 88-2SIOJP blocks the SMEMR signal on the S-100 bus by asserting
the Status Disable signal, STSBn. While this signal is asserted, the
Altair CPU does not drive any of the 8 status signals. (These signals
are SINP, SOUT, SINTA, SMEMR, SWON, SHLTA, SSTACK, and SM1. Note that
SMWRITE is not on this list, as it is generated by the Altair front
panel.)"

I haven't used the 88-SIOJP in a while, but I seem to remember that I need to hit reset on my machine before it jumps into the monitor. I'll re-install it tomorrow and refresh my memory.

I've seen a reset button on the 9 slop backplane, could that not be used to do the jump start?
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Re: Altair 8800C without front panel

Postby AltairClone » July 25th, 2022, 3:40 pm

I think you'll need a newer version of the 2SIOJP, a front panel board, or a newer CPU board that doesn't require front panel signals.

Here's a link to a 2SIOJP manual that covers the different versions and talks about the features to support systems without a front panel.

https://deramp.com/downloads/mfe_archiv ... mplete.pdf

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Re: Altair 8800C without front panel

Postby TheoAU » July 26th, 2022, 5:09 am

Thanks for the reference to the versions of the 2SIOJP. Yes, it looks like I got one of the very first versions. It's impressive the amount of features that have been added since. My only consideration in running with no front panel was so I can do the 8800C in stages, first the CPU, then the motherboard and then front panel and case. But I do intend on having a front panel with the finished machine.
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