🚀 go-pugleaf

There was some discussion about the asynchonous mode operation of 80387 a while ago, I don't remember what the conclusion was. I have a related question, perhaps someone would care to comment.

According to Intel's publication "Microprocessor and peripheral handbook p. 4-148.":  when pin CLKM=1, NPX387 works in synchronous mode, CPUCLK2 is used to control the 387; when CLK1=0 (asynchronous mode), NUMCLK2 is used to control the 387, provided NUMC
LK2 : CPUCLK2  is between .625 and 1.4.

I know some of Micronics's MB is impplemented such that you can install a seperate crystal to supply this NUMCLK2.

Given all this, why should I bother to puchase a 25 Mhz 387 to work on my 25Mhz 386 MB. A 20 Mhz 387 is perfectly within the specifications published by Intel, unlike the 25Mhz push of 20Mhz 386 cpu. So reliability does not appear to be an issue, it seems
 to me. Granted, MIPS magazine had reported on 33 Mhz systems using 387-25 was slower when compared with 387-33. Other than that, are there other ramifications on using lower rated 387 on faster 386 MBs?

Anybody care to enlighten me on this subject!


kuo@oregon.uoregon.edu