IMSAI-duino (Phoenix)

[Bob senzig]

I have seen a lot of variations of the Altair front panel. I know this is off topic but I thought it would be of interest. I am trying to adapt an original IMSAI 8080 front panel to the Altair-duino emulator.

Back in the day 1975ish I built an S100 based system using a Jade Z-80 CPU card. I wanted to add a front panel. I found a IMSAI front panel for sale and bought it for $60. I wired it to my S100 bus. It was a nice CP/M system and sported a 1.2Mb removable platter hard disk. and an 8 inch floppy. Eventually I sold the entire system to some kids at a swap meet that wanted to experience the original personal computer experience. I kept the front panel. I was just going to put a strip LED until I found the emulator. I am getting help from some local friends, but I'm hoping that I might also get some help here. There is not a 1:1 correlation of the satus LEDs and control switches. I am disabling all the logic on the IMSAI board so it will just be switches and LEDs. Wish me luck

Attached is a 1982 photo of my home computer with my son trying to play with it. That's a DG NOVA 2 he's programming. The IMSAI is higher in the rack.

[Tom Wilson]

The mapping is very close, but not exact. We can help you modify the firmware to make ir closer, if you want. You’d definitely want to get the new I/O board and add the LED output board to map the Programmed Output LEDs. 

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Tom Wilson
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(619)940-6311 

[Walt Perko]

Hi,

Maybe instead of crapping out a real IMSAI front panel, get the IMSAI mini-Front Panel board from Don Caprio ... about $30 including shipping.  

Don also sells the full size CPA front panel blanks too ... about $35 including shipping.  

I have one of each, they're great and starting with a blank board you can probably build a piggyback wirewrap board to configure to the Altair-Duino.  

The IMSAI mini-Front Panel:  

The IMSAI Reproduction CPA Front Panel:  

I'm still waiting for the new switches with blue and red paddles ... a special batch order from NKK ... 

It's just sad when people butcher vintage computer boards and even the computers.  

There's a guy in the S-100 group that bought an original Altair 8800 to find the power supply isn't original and is a piece of butchered crap.  

.

[Bob senzig]

Interesting perspective. Perhaps you missed the nostalgia part of this "crapping out" job. This is the front panel from a machine I built and used many years ago. I hated to decommission it but had to for space and focus 3 decades ago. I no longer have any other parts. The boards that used to be in it were sold when decommissioned or were donated to the Computer History Museum in CA. 

I plan to rework it with just removing the chips and doing the "crapping" on a separate board. When I'm dead and gone and someone wants to rebuilt it to original, it could be done.

[Bob senzig]

Tom,

I'll post my progress and any issues. Here is what I am thinking.

[Walt Perko]

Hi, 

I was thinking that a good original IMSAI front panel is worth more on eBay than a new reproduction modified for the Altair-Duino.  I'm sure you could get at a minimum $100 for that front panel on eBay so somebody could repair or refurbish another machine, while you modify an Altair-Duino into an IMSAI.  

.

[Bob senzig]

Thanks for the economic advice. But, I am not interested in getting a new machine but reanimating the one I have that was my “first” computer. That is why I kept it. I bought it second hand to install in my genetic S100 system. It had some IMSAI mechanical parts missing. I supplanted the missing parts and made it so it would mount in my relay rack. I doubt any eBay value as it is not original already. 

Sent from Outlook for iOS

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From: altair...@googlegroups.com <altair...@googlegroups.com> on behalf of Walt Perko <r4r...@gmail.com>
Sent: Saturday, March 25, 2023 6:57:45 PM
To: Altair-Duino <altair...@googlegroups.com>
Subject: Re: IMSAI-duino (Phoenix)

 

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[wils...@gmail.com]

Hey, Bob.

So looking at my Imsai Replica, here are some thoughts (which you may have already addressed, not sure...)

The command switches (bottom row of switches on the Altair, or the right 5 switches on the IMSAI) are the same, just in a different order. You can wire those to the Arduino, and those will work fine. However, 2 switches do not exist on the IMSAI: the two AUX switches. You can operate without these, but you'll need my modified "B" firmware, with some additional changes. 

The status LEDs are the same, excepting the INTE, PROT, WAIT, and HLDA pins. They don't exist on the IMSAI. 

So with the 4 missing status LEDs and the 4 missing switch contacts, you have a total of 8 extra lines. These can be used for the Programmed Output. 

So this leaves the question of "How do I use the menu?" Which is valid. I have modified my Altairduino B model with a Stop mode menu, which gives me access to the full set of front panel commands, including the setup menu, without the need for physical switches. Turning that on will let you open the Configuration menu and swap drives or access the bundled sample programs. 

Here's my fork:

https://github.com/tomxp411/Altair8800

So the needed changes to the firmware would be: 

1. Remove the connection to the AUX switches and make those the lower nibble of the Programmed Output LEDs

2. Change the 4 INTE, PROT, WAIT, and HLDA LEDS to be one nibble of the programmed output byte

3. Intercept writes to Port 0xFF to set the 

4. Set "Serial Console" locked on.

5. Add the Stop mode menu from my fork.

The "B" mode changes from my fork won't do anything for you, since they solely change the behavior of the Aux switches, so I'd just grab the menu changes and use David Hansel's main branch as the starting point for your version. 

[Bob senzig]

Wilsontp,

Thanks, This is very helpful info. It would have stumped me for sure. The Menu tip is tremendous/. 

I'm curious why you decided to build an IMSAI replica and not an Altair one? I used the IMSAI front panel in my generic s100 system because it simply plugged into the S100 bus I had. The data ribbon cable was compatible with the JADE Z-80 kit CPU I built with a clock mod it ran at 4Mhz. 

I also have an early homebrew Altair kit (built from the 1975 original bare boards MITS sold) but if I tried to turn that on it would probably halt and catch on fire. 

[Tom Wilson]

I already had 3 Altairduinos. The IMSAI 8080 Replica, from The High Nibble was the next logical step. =)

I don’t necessarily recommend it for your project, because it needs bit shifters. The Arduino Altair 8800 emulator is a great choice for rolling your own panel. 

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