View Full Version : Another recovering IMSAI 8080

January 12th, 2015, 02:29 AM

Time to de-lurk!

Woot - After gearing up for whet feels like 10 + years, I have finally been able to score an IMSAI 8080 chassis with front panel. It is in pretty good condition, but bare - there are *no* boards present. That was not a worry, as in about 2009, I brought a set of Solata boards from eBay that were unpopulated.

So far, I have populated the Solata CPU card which has provided me with a functioning Z80-A cpu, and a Solata mixed memory card to give me 2K of RAM.

With a little love being applied to the front panel, I can now single step the CPU, deposit data into memory, examine from memory, and output data on the 8 LEDs on the front panel. I currently can't read from the front panel port (at location 0xff), but that can't be complex :-)

I have ordered a 65K dynamic memory card, and just have to sort out a SIO card. I do have the Solata 2S+P card that just needs to be populated, or I can pick up an actual IMSAI card from ePay.

In all, I am getting there :-)

A couple of questions:

1. Comparability with IMSAI software is important - A cursory glance of the Solata board looks like it may be compatible with the IMSAI SIO, but does anybody here know for sure?
2. My machine has the 110V only PSU - I am in Australia..... While I am currently running through a step down transformer. Does anybody know where I can source the transformer that had the dual primary windings? I don't mind paying shipping from the USA.
3. I was 2 days late to the auction site, and missed out on a red paddle lever - The right hand red paddle is partially broken - I have an email in with Todd Fischer from the new incarnation of IMSAI, but there has been no response. Can anybody assist with a replacement?

I know I currently have an IMSAI box, and a bunch of non IMSAI parts - I am wrestling with what is actually important to me?? Do I want an *actual* period correct machine, or something that looks wonderful and is functional? I am willing to accept guidance from others. I have a substantial collection of old gear, including a PDP11/10, a 11/34, a heap of other machines from the mid-late 70's including TRS-80's, Apple IIs, Comodore 64's, and a Dream 6800 and am very happy to have this machine compliment my world.

Doug Jackson

January 12th, 2015, 04:58 PM
Is it one of the red address paddle levers you are needing, or is it the power on-off switch all the way on the right? If it's the address style switch, PM me, I've got one and will send it to you. It's an original, so there are some scratches.

January 12th, 2015, 09:58 PM
It is a red Addrerss one - That would be wonderful.

My account here doesn't have permissions to PM yet, so my email is:

doug at doughq dot com


January 13th, 2015, 02:43 AM
Congratulations on getting your IMSAI! I know what it's like to pursue something and finally get it.

I don't have any of your answers other than I've purchased paddle switches from eBay and it wasn't through Todd Fischer but looks like new_castle_j has you taken care of.

It's a matter of preference but I like to keep my equipment stock or upgraded but reversible to get it back to stock. As for keeping the IMSAI 8080 with it's original cards, think of it as a continued pursuit to find those cards. You can enjoy it with the Solata cards for now but it will be a whole new machine when you can find those cards. Hopefully, it won't take another 10 years :)

January 14th, 2015, 01:02 PM

I think that is the best plan - The *reality* is that we all upgrade and improve machines as we go along. I love the idea of making sure it is able to be reverted if required - even if the cards sit in protective boxes normally.

I am having trouble PMing people - So I am not confident that new_castle_j got my message, so I will just mention it here. Do you know how to contact the board admins to identify the source of the PM issue?


January 17th, 2015, 10:56 AM

I have just had a quick look at the technical specs. for both the IMSAI SIO2 and the Salota 2S+P card and they are 'almost' compatible!

Both cards utilise the same USARTS (Intel 8251) however the two USARTS are addressed slightly differently between the two cards. Address line A0 selects the Control (1) or Data (0) register within the 8251 USART - but the selection mechanism for USARTS A and B differ between the two cards. USART A is selected when A1=0 and USART B is selected when A1=1 for the Salota card; whereas USART A is selected when A1=1 and USART B is selected when A2=1 for the IMSAI card.

The bottom line is that you may be able to use the 'B' USART on the Salota card to map onto the 'A' USART of the SIO2 as they are both addressed at the same relative offset within the block of 16-bytes of space allocated to the card. This does (however) assume that interrupt are not used - as there appears to be some differences here as well. You may not be able to utilise both USARTS on the card by off-the-shelf software as a result of the addressing differences. However, I have only just had a quick look...

The other thing you need to be aware of is that software designed to run on an Intel 8080 CPU may not run on a Zilog Z80. The classic example of this was the early ALTAIR basic if memory serves me correctly. Some of the instructions treat the flags differently between the two processors - so you can sometimes run into trouble.


April 5th, 2015, 04:19 AM
Hi, Just restoring another one I Australia; have you managed to get a transformer that had the dual primary windings?