Sir_Fartalot

March 9th, 2016, 06:13 AM

Dear all,

I want to add a numerical (mathematical, math) coprocessor co-processor to my motherboard which has a soldered-in 386SX running at 33MHz. More exactly, it is an AMD Am386 SX/SXL-33. The problem is that I have a 387SX running at 20 MHz, so I will have to set up my motherboard for asynchronous work with the NPU.

The motherboard is probably a Biostar MB-1325/1333ACA-S. I say "probably", because I could only determine it by looking at the images of 386 motherboards on Total Hardware. The closest one is http://www.uncreativelabs.de/th99/m/A-B/32442.htm

While some important elements of my motherboard are missing from that diagram, all the jumpers seem to be in the correct locations, so I will work on the assumption that I found my motherboard.

If you look at the page I linked to, you will see that I have to set jumper 7 to close pins 2 and 3 ("Clock mode select asynchronous"). That's the easy part! What you don't see on that diagram is that there is a socket for a crystal oscillator to the left of the 5th and 6th ISA slot. It is marked with "OSC 1". I assume but am not sure that I need to put an oscillator in there, so that the NPU can work at its own frequency. I also assume but am not sure that the frequency of the oscillator should be 20 MHz. However, note that often with motherboards there are frequency dividers and multipliers.

Can you please help me clarify whether my assumptions are correct? Many thanks in advance.

Oh, and BTW, this is my first ever post in this forum.

I want to add a numerical (mathematical, math) coprocessor co-processor to my motherboard which has a soldered-in 386SX running at 33MHz. More exactly, it is an AMD Am386 SX/SXL-33. The problem is that I have a 387SX running at 20 MHz, so I will have to set up my motherboard for asynchronous work with the NPU.

The motherboard is probably a Biostar MB-1325/1333ACA-S. I say "probably", because I could only determine it by looking at the images of 386 motherboards on Total Hardware. The closest one is http://www.uncreativelabs.de/th99/m/A-B/32442.htm

While some important elements of my motherboard are missing from that diagram, all the jumpers seem to be in the correct locations, so I will work on the assumption that I found my motherboard.

If you look at the page I linked to, you will see that I have to set jumper 7 to close pins 2 and 3 ("Clock mode select asynchronous"). That's the easy part! What you don't see on that diagram is that there is a socket for a crystal oscillator to the left of the 5th and 6th ISA slot. It is marked with "OSC 1". I assume but am not sure that I need to put an oscillator in there, so that the NPU can work at its own frequency. I also assume but am not sure that the frequency of the oscillator should be 20 MHz. However, note that often with motherboards there are frequency dividers and multipliers.

Can you please help me clarify whether my assumptions are correct? Many thanks in advance.

Oh, and BTW, this is my first ever post in this forum.