View Full Version : Imsai RAM board

August 8th, 2010, 04:04 PM
Hi all !

I recently acquired an Imsai 8080 machine and I'm
looking to get it up and running.

It came with only a CPU board 8080 rev-4 and a Expandoram II
memory board. I also picked up a Microbyte 32k board from ebay.

I'm not sure if either one of these boards are compatible with the 8080.
I know from the docs I read about the Expandoram it mentioned z80 so
maybe it wont work with my system (bought as-is)

The problem I'm having is that I can't deposit to memory and
examine it back, the data LED's are all high no matter what I do.

So I'm wondering if its a memory issue or something else. I've verified
voltages and sniffed around with a logic probe (thinking a bad IC
on the front panel pulling the data bits high)

To sum it up, since the CPU board doesn't have any memory, I guess
I need to know if the memory boards I have are compatible. Maybe
there both bad. I don't want to chase my tail, been doing that for a week
already ;-)

Anyone have a suggestion or perhaps a static ram board for sale
so I can continue debugging this machine.

I also posted to the s100computers forum with a bit more
detail earlier in the week.


Dwight Elvey
August 8th, 2010, 09:57 PM
I have an Expandoram II working with an 8080.
It is a Polymorphic CPU board though. The Expeandoram
has the built in refresh so doesn't need the Z80's refresh.

August 9th, 2010, 06:53 PM
I guess I don't understand the dip switch settings for the expandoram II.
How should I set the switches for my Imsai, just one memory board installed.
The board is set up for 64k. I'm not sure I understand what the 'banking' is all
about, if someone could explain. http://home.mchsi.com/~litterbox99/graphics/dip1.jpg

Dwight Elvey
August 10th, 2010, 06:20 AM
Banks are use when you want more than 64K on the bus.
The banks are controlled by one of the I/O ports ( I forget
which ).
You expect to use all of the memory so I'd say that you'd
want to turn it all on. I think for that board, there are 4
16K banks.
If you have ROM in your system, I believe the board uses
the Phantom signal to disable the RAM for that part of
memory so that it doesn't conflict.

August 10th, 2010, 12:46 PM
Banks are use when you want more than 64K on the bus.
The banks are controlled by one of the I/O ports ( I forget
which )40H is often used.

August 16th, 2010, 09:29 PM
In the infamous words of Gene Wilder... 'It's Alive !'

Today I received a Godbout 8k static RAM board from ebay and a bunch of parts
from digikey & jameco. I replaced all the caps on the MPU, a few bus driver IC's
and the 8212 IC. I was able to deposit & examine data into memory & verify !
I toggled in a 'chase LED' program I found on the net by Lawrence Woodman.

I must have toggled that program in about six times before I realized that my first
deposit into memory should have been a deposit, and not a deposit next. YeeHaw,
the program worked ! I'm so excited :-) I hated to turn the dang thing off.

Here's a link to a short video I made. It's an .avi file and it's the first vid I've
done so if it's to long or big, sorry about that.


Well it's late and I've been up since 4AM (had to take the girlfriend
to the airport so she could see her ma in Sacramento) So I'm gonna
call it quits ! If you would like to see my other hobby check out;


Thanks guys !