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Tandy 286 Express Accelerator and 80287 math coprocessor issues

J

jasa1063

Experienced Member
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Jan 5, 2015
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386
Location
Minnesota, USA
I recently got a Tandy 286 Express accelerator and installed in my Tandy 1000 SX as posted in this thread:


Everything is working great after swapping out all them memory in Tandy 1000 SX, but I still had one issue. The computer would freeze using a 80287 math coprocessor. I tried two different 80287 chips and they both did the same thing. I changed the dip switch settings for a 5MHz 80287, but that did not help either. I finally installed 80287XL and that seems to almost totally fixed the issue except that CheckIt still locks up the Math Speed test. I have tried versions 1.1, 2.1 and 3.0 and get the same result. All other benchmarking and software that uses the a math coprocessor works normally. I have run CheckIt 3.0 with a 80287XL in my Tandy 1000 TX, TL/2 and TL/3 and those work just fine. Any ideas on why this maybe happening?
 
I have a SX with a NEC V20 and a co-processor which runs Checkit with no issues. I'm inclined to think that there may be an issues with checkit and the 286 card. Try pulling the 286 card and then run Checkit with co-processor installed on the motherboard.
 
Agent Orange said:
I have a SX with a NEC V20 and a co-processor which runs Checkit with no issues. I'm inclined to think that there may be an issues with checkit and the 286 card. Try pulling the 286 card and then run Checkit with co-processor installed on the motherboard.
Click to expand...
I used the PCT utility to switch back over to the 8088 CPU and CheckIt works fine. That gave me an idea to switch back the 286 CPU, but disable the 8K cache. Well what do you know, CheckIt works just fine doing that. So the Cache as used on the Tandy 286 Express Accelerator is not compatible with CheckIt and the Main System benchmark. CheckIt does work doing the System Board test which tests the math coprocessor. I am just glad to have figured it out.
 
Last edited:
jasa1063 said:
I used the PCT utility to switch back over to the 8088 CPU and CheckIt works fine. That gave me an idea to switch back the 286 CPU, but disable the 8K cache. Well what do you know, CheckIt works just fine doing that. So the Cache as used on the Tandy 286 Express Accelerator is not compatible with CheckIt and the Main System benchmark. CheckIt does work doing the System Board test which tests the math coprocessor. I am just glad to have figured it out.
Click to expand...
Great! Do you have Lotus 1-2-3 which can utilize the co-processor? That, and once upon a time I had a CAD program that would work with it. The 486DX pretty much put the add-on FPU's out to pasture.
 
Agent Orange said:
Great! Do you have Lotus 1-2-3 which can utilize the co-processor? That, and once upon a time I had a CAD program that would work with it. The 486DX pretty much put the add-on FPU's out to pasture.
Click to expand...
I do have Lotus 1-2-3, but I am using the one for DeskMate. I don't know if that uses the Math Coprocessor or not.
 
I used Borland's Quattro Pro on my 1000A with the 286 express. Had to disable the cache for that to work too. It was obvious when the math coprocessor was running in Quattro Pro.
I was doing groundwater modeling as a school project and I needed all the horsepower I could afford. Deskmate did not use the 8087.
 
I have a couple of Mandelbrot programs that I modified a few years ago with inline assembler routines for the fast FPU execution. I can run those all day long with the cache enabled and not a single problem. It's just strange that there seems to be a certain combination of FPU instructions that cause it to freeze up.
 
I swapped out the Intel 80287XL math coprocessor for an IIT 2C87. Now CheckIt is working normally and I have not had any other problems. You would think that an Intel math coprocessor would the one not to have compatibility issues, but I am just glad to have found a solution.
 
jasa1063 said:
I swapped out the Intel 80287XL math coprocessor for an IIT 2C87. Now CheckIt is working normally and I have not had any other problems. You would think that an Intel math coprocessor would the one not to have compatibility issues, but I am just glad to have found a solution.
Click to expand...
Maybe the issue is just with that particular FPU.
 
Agent Orange said:
Maybe the issue is just with that particular FPU.
Click to expand...
I had previous tried a 10MHz 80287 from another computer that I know works and had the same issue. I also tried two different 80287XL math coprocessors and got the same result and those worked with no issue in other 286 computers I have. I just think there are compatibly issues with the onboard 8K cache on the Tandy 286 Express accelerator in general.
 
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