smp
Veteran Member
Hello all,
I decided to spend some time with my IMSAI today, to attempt to get to the bottom of my suspected memory problems.
My IMSAI consists of:
Compupro CPU-Z
Compupro RAM-17
S100 Computers SIO
I also have the original IMSAI 8080 CPU card (MPU-A rev 4) and a few Compupro Econoram II 8K RAM boards. Plugged into one of the 2K RAM spots at F000H on the RAM-17, I have a system monitor EPROM that I cobbled together from the TDL Zap monitor and an Intel Hex file loader I also found out on the Internet.
Here's the scenario:
I can power up the system and run the system monitor to my heart's content. I wrote a simple memory test to load memory with AAH and read back, then alternate to 55H and read back, and go again and again for days on end. Not a great test, but it builds some confidence.
A while ago (many months, probably a couple of years), I acquired a Northstar floppy disk controller and some good folks here assisted me with getting a couple of boot disks. I struggled mightily with the controller but I could not get it to work fully. It seemed to be able to read disks properly but when I attempted to write to disk, it would destroy all data on the disk making it unusable. A nice fellow here volunteered to try the disk controller in his machine, and reported that the controller was fully functional in his system. That was good news, but discouraging for me as I could not get it to work in my system. Discouraged, I sold off the controller along with a bunch of other S-100 boards I had gathering dust, but I retained the IMSAI as described above. I figured that I had a memory problem of some sort, but I didn't have much of a clue of what to do next.
Here I am today:
My first try was to load a copy of IMSAI 8K BASIC that I have set up for my machine. Download seems to go fine, but BASIC doesn't run. I suspected the first step was to bring the CPU-Z down to 2 MHz instead of 4 MHz. That didn't seem to do much of anything for me. I fiddled around with the front panel to discover that when I reset the computer, it did not start at address 0 but at address 1. Since the CPU-Z is set to auto-jump up to F000H to run my system monitor, I didn't see that before. I replaced the CPU-Z with my IMSAI 8080 CPU to see that the address bit was no longer "stuck." I put "stuck" in quotation marks because I can still load my little memory test program hex file from my system monitor and get that to go just fine.
Since something does seem to be up with the RAM-17 board, I decided to try to put a couple of my Econoram IIs in the first 16K, leaving the upper 48K active on the RAM-17 board. It's a good thing that I have three of these Econoram IIs because only one was tagged as good, and the others were tagged as questionable. The good one did seem to be good. The second one had some issues, but with a few rounds of memory fill and memory dump, I was able to replace a couple of RAM chips with chips from the third board and seemingly get a couple of the Econoram IIs "working."
I tried loading the 8K BASIC again, and I got it to work - kind of. BASIC seemed to be working in immediate mode, but I could not type in a program - it would hang up when I entered the first carriage return on a line with a line number on it. Hoping for a break, I switched the two Econoram IIs and things got worse, but I found that one of the 4K banks of RAM was not responding, so I suspected the dip switches might be glitchy. A few more tries with changing the banks around and I made it to the point that I am now:
I can load IMSAI 8K BASIC and run it. I can type in a program and list it and I can run it. I can load a program by sending a file into the computer from the terminal and I can list it and I can run it.
For me, this is great progress, but I do not trust that I actually have solved anything really. It appears that I have the bottom 16K RAM working, but this has by no means been an exhaustive test. I have run my simple memory test on the RAM-17 board and also on the two Econoram II boards. My current situation has the two Econoram II boards as the bottom 16K RAM, the 16K RAM from 8000H to BFFFH on the RAM-17 is currently disabled to keep BASIC only using the lower 16K RAM, and the upper 16K RAM on the RAM-17 is not being used, except for the 2K occupied by my system monitor EPROM. Something is up with the RAM-17, but I do not currently have a tool to sniff it out. It's nice to see BASIC running in the IMSAI, but I am not entirely certain about the two Econoram IIs, either. They also should be thoroughly checked out.
Does anyone have a good memory test program that I might be able to download from somewhere as an Intel Hex file? If I could get a good tool, at least I might be able to build more confidence in my memory boards - or find the weaknesses and get them fixed, so I can build more confidence.
If I can only get a good set of memory in this thing, then I will be in a good position to finally move on and try another disk drive controller.
Thanks, in advance, for any advice or comments that you may have for me.
smp
I decided to spend some time with my IMSAI today, to attempt to get to the bottom of my suspected memory problems.
My IMSAI consists of:
Compupro CPU-Z
Compupro RAM-17
S100 Computers SIO
I also have the original IMSAI 8080 CPU card (MPU-A rev 4) and a few Compupro Econoram II 8K RAM boards. Plugged into one of the 2K RAM spots at F000H on the RAM-17, I have a system monitor EPROM that I cobbled together from the TDL Zap monitor and an Intel Hex file loader I also found out on the Internet.
Here's the scenario:
I can power up the system and run the system monitor to my heart's content. I wrote a simple memory test to load memory with AAH and read back, then alternate to 55H and read back, and go again and again for days on end. Not a great test, but it builds some confidence.
A while ago (many months, probably a couple of years), I acquired a Northstar floppy disk controller and some good folks here assisted me with getting a couple of boot disks. I struggled mightily with the controller but I could not get it to work fully. It seemed to be able to read disks properly but when I attempted to write to disk, it would destroy all data on the disk making it unusable. A nice fellow here volunteered to try the disk controller in his machine, and reported that the controller was fully functional in his system. That was good news, but discouraging for me as I could not get it to work in my system. Discouraged, I sold off the controller along with a bunch of other S-100 boards I had gathering dust, but I retained the IMSAI as described above. I figured that I had a memory problem of some sort, but I didn't have much of a clue of what to do next.
Here I am today:
My first try was to load a copy of IMSAI 8K BASIC that I have set up for my machine. Download seems to go fine, but BASIC doesn't run. I suspected the first step was to bring the CPU-Z down to 2 MHz instead of 4 MHz. That didn't seem to do much of anything for me. I fiddled around with the front panel to discover that when I reset the computer, it did not start at address 0 but at address 1. Since the CPU-Z is set to auto-jump up to F000H to run my system monitor, I didn't see that before. I replaced the CPU-Z with my IMSAI 8080 CPU to see that the address bit was no longer "stuck." I put "stuck" in quotation marks because I can still load my little memory test program hex file from my system monitor and get that to go just fine.
Since something does seem to be up with the RAM-17 board, I decided to try to put a couple of my Econoram IIs in the first 16K, leaving the upper 48K active on the RAM-17 board. It's a good thing that I have three of these Econoram IIs because only one was tagged as good, and the others were tagged as questionable. The good one did seem to be good. The second one had some issues, but with a few rounds of memory fill and memory dump, I was able to replace a couple of RAM chips with chips from the third board and seemingly get a couple of the Econoram IIs "working."
I tried loading the 8K BASIC again, and I got it to work - kind of. BASIC seemed to be working in immediate mode, but I could not type in a program - it would hang up when I entered the first carriage return on a line with a line number on it. Hoping for a break, I switched the two Econoram IIs and things got worse, but I found that one of the 4K banks of RAM was not responding, so I suspected the dip switches might be glitchy. A few more tries with changing the banks around and I made it to the point that I am now:
I can load IMSAI 8K BASIC and run it. I can type in a program and list it and I can run it. I can load a program by sending a file into the computer from the terminal and I can list it and I can run it.
For me, this is great progress, but I do not trust that I actually have solved anything really. It appears that I have the bottom 16K RAM working, but this has by no means been an exhaustive test. I have run my simple memory test on the RAM-17 board and also on the two Econoram II boards. My current situation has the two Econoram II boards as the bottom 16K RAM, the 16K RAM from 8000H to BFFFH on the RAM-17 is currently disabled to keep BASIC only using the lower 16K RAM, and the upper 16K RAM on the RAM-17 is not being used, except for the 2K occupied by my system monitor EPROM. Something is up with the RAM-17, but I do not currently have a tool to sniff it out. It's nice to see BASIC running in the IMSAI, but I am not entirely certain about the two Econoram IIs, either. They also should be thoroughly checked out.
Does anyone have a good memory test program that I might be able to download from somewhere as an Intel Hex file? If I could get a good tool, at least I might be able to build more confidence in my memory boards - or find the weaknesses and get them fixed, so I can build more confidence.
If I can only get a good set of memory in this thing, then I will be in a good position to finally move on and try another disk drive controller.
Thanks, in advance, for any advice or comments that you may have for me.
smp
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