80187 pin compatible with either 8087 or 80287?

[black_monolith]

The 80187 is the only FPU that I have never used. From what I gather they came out much later than the 80186 (something like 1989) and were mostly used in microwaves and controllers. On paper it seems very similar to the 80287XL. I have always wondered if the 80187 could work in 8086 or 286 systems, but I have never had one to try.

From what I know 8087 works with 8086, 8088, 80186 or 80188. Strangely the 80187 is said to work with an 80186, but not an 80188. The 8087 could auto detect 8 or 16-bit mode, but apparently the 80187 would only work on 16-bit buses (80188 uses an 8-bit external bus).

However, the 8086 chip is also 16-bit. I am curious if it is able to cooperate with an 8087. Does anyone know the answer?

[black_monolith]

I think I may have found the answer. The 80187 works with none of the above, not even the regular 80186. It requires a special version, the 80C186. Weird.

[joekster]

From what I remember reading, a regular 8087 would work with the 80186/80188. Unless there is something "special" about the 80187, I think its just a rebadged 8087. I'm also 99.999% sure a 287 would NOT work with an 80186/80188.

[black_monolith]

You are correct that a 287 would not work with an 80186/80188. But I have a feeling it may work with an 80C186. There is something different about the 80C186 than just the CMOS process. It's been a while since I last compared datasheets of the 80187 and 80287, but they were nearly the same or identical from what I recall. Infact, the 80187 is closer to the 80287XL since it incorporates all the features of the 80387.