cyang%peruvian.utah.edu@cs.utah.edu (Cheng Yang) (12/20/90)
Hi, everybody. I am very thankful that I have got a bunch of helpful replies from you regarding to the AMD 80C287. I just called the dealer and I have another problem. On the manual of my motherboard, it said that " To determine which speed 80287 is needed, purchase the one that can operate at 2/3 the maximum speed of your motherboard. The IBM AT computer is designed to use the pin on the 80287 that devides the crystal frequency by 3. The 80286 devides the crystal frequency by 2 to obtain the system clock speed. .... " and it recommend I use 80287-10 to work with my 16MHz 80286. Actually the crystal frequency on my motherboard is 32 MHz. So the coprocessor will get 10.67 MHz.(not exactly 10 MHz) (My motherboard is bought over one year ago and there was few 12 MHz coprocessor at that time, I think.) The dealer I talked to said that I need an AMD 80C287-12 which is $139.00. And he said that the $99.00 AMD 80C287 is 10MHz and it is for 12 MHz 286 or less.. My question is: Who is right? My manual or the dealer. What will the result be if I put that 10MHz AMD 80287 on my motherboard, will the 10.67MHz hurt the 10MHz 287? Or the chip won't work totally? Do I really need a 12MHz coprocessor??? I will be very appreciated if you can give some advice. Thank you very much for your time in advance. ***************************************************************************** * Ho capito, signor,si!........ * * * *Cheng Yang Home Address: * *Department of Computer Science 808 East, 300 South, #3 * *University of Utah Salt Lake City, UT 84102 * *E-Mail Address:cyang@peruvian.utah.edu Tel: 801-322-1918 * *****************************************************************************
phil@brahms.amd.com (Phil Ngai) (12/20/90)
Making semiconductors is a little like trying to figure out how much sleep people need. Some people need more than others. Everyone will need more or less depending on how much they did that day (hard day chopping wood or easy day relaxing?). Semiconductors generally can run faster when they are cooler (there's a company, Velux, that sells chip coolers to let you push your processor). Also the factory includes at least a little extra margin to guarantee the chip will work at spec. If the "yields" are good, there may be a lot of margin. As the product matures, the average speed will probably go up from process and design improvements and tweaks. Can you use a 10 MHz 287 at 10.67 MHz? Maybe, maybe not. It is less than 7% over so I wouldn't be surprised if it did work. All you KNOW is that if you try it and it doesn't work, the factory will not consider the device to be defective. It is very unlikely that any physical damage would be caused by such an experiment. This is my opinion exclusively and I do not speak for the company or work anywhere near that group. Someone ought to put this kind of discussion in the list of frequently asked questions, if it isn't already. --
rfutscher@pbs.org (12/21/90)
In article <1990Dec19.121014.3338@hellgate.utah.edu>, cyang%peruvian.utah.edu@cs.utah.edu (Cheng Yang) writes: > > Hi, everybody. I am very thankful that I have got a bunch of helpful > replies from you regarding to the AMD 80C287. I just called the dealer > and I have another problem. > > On the manual of my motherboard, it said that " To determine which speed > 80287 is needed, purchase the one that can operate at 2/3 the maximum speed ^^^^^ > of your motherboard. The IBM AT computer is designed to use the pin on the > 80287 that devides the crystal frequency by 3. The 80286 devides the crystal > frequency by 2 to obtain the system clock speed. .... " and it recommend I > use 80287-10 to work with my 16MHz 80286. Actually the crystal frequency > on my motherboard is 32 MHz. So the coprocessor will get 10.67 MHz.(not > exactly 10 MHz) (My motherboard is bought over one year ago and there > was few 12 MHz coprocessor at that time, I think.) > > The dealer I talked to said that I need an AMD 80C287-12 which is $139.00. > And he said that the $99.00 AMD 80C287 is 10MHz and it is for 12 MHz 286 or > less.. > > My question is: Who is right? My manual or the dealer. What will the result > be if I put that 10MHz AMD 80287 on my motherboard, will the 10.67MHz hurt > the 10MHz 287? Or the chip won't work totally? Do I really need a 12MHz > coprocessor??? > I purchased a ITT 287, and it would not pass the test that came with it. A replacement ITT 287 failed the test the same way. Like your motherboard the clock for it was also an uneven division, which made the duty cycle of the clock 1/3, 2/3. If the duty cycle was 1/2, 1/2 I am sure that it would pass the test. I am sure an Intel 287 would pass the test with a duty cycle of 1/3, 2/3. With clone 287 you need to be aware of duty cycles that are not 50/50.