8088, 286 CPU upgrade, general chat

  • Zitat von V3SDave

    Whaaaaat an 8088 Upgrade 8| :love: :love: What i have to do ?

    Let's keep the 386P upgrade thread clean from other CPU upgrade possibilities, so I started another topic. Didn't realize there was interest for this!

    Yes, the NEC V20, V20HL and I suppose V30, too, would be all suitable as performance adding replacements, but that all allow also lifting of the clock speed: get one, and plug it in and make tests before and after.

    For example, make a program that has a lot of 3D countouring and see how the machine performs and time how long does it actually take to finish the task. Then plug the upgrade in, and run the same test run again and compare the times and visually compare if there is any difference in "jerking motion".

    I found a rather good image of a 8088 CPU board, not sure if yours is the same though, I believe you run a 432/9 control, I'm completely unfamiliar with that.

    Anyway, let's assume that the board is the very same and only difference are the EPROM's, if even them: We can see that there is only one oscillator running at 24 MHz. As we know from the 386 upgrade topic, there, too, is a 24 MHz crystal oscillator and we know that it runs there only the control bus and that three different frequencies are made based on that 24MHz by a ripple counter chip that gives out 1.5, 3.0 and 6.0 MHz frequencies.
    Now that we see only one oscillator, we can only assume that there is only one oscillator to give clock frequency to whole system. This possibly makes raising the CPU frequency a quite much more difficult task and without having the PCB layout / repair diagnostics documentation, it is impossible to say how the clocking is being issued on that board.

    If/when there is a clock processing chip somewhere on the board (those P8253 at the bottom right are timing devices with two clock inputs), it would be beneficial to know if the memory operations and CPU are using the same clock speed, then it could be possible to make simple modification on board that there would be a separate clock for previous operations and leave the control bus handling alone. Simpliest way to make this, I guess, would be installing an extra socket under the CPU and cut off the CLK signal and do the same for the clock processing chip and cut off the clock signal that handles CPU etc and install a separate oscillator and ripple counter (for example) to be used used to input clock signal to cpu etc. I guess a separate test PCB would do the trick.

    Those P8253 suggest that timing logic is similar to what the DMA controller on 386P board does, I _guess_.

    8088-2 in the picture can run at 8MHz. If the clock processing is the same as in 386P, then it would probably run at 6MHz. It could also run at 8MHz (24/3). Latter might be the case if the unreadable chip to the right next to the oscillator is a D8284, as it divides the oscillator frequency by three (1/3). Its datasheet says that it provides clock signal to CPU and to all bus devices that are connected to CPU. I think it's highly unlikely that the control bus speed would be 8 or even 6MHz as more modern control has 1,5/3M clock, but by those pics, I can't say where else clock signals are being processed/generated.

    I suppose that 24MHz clock is a legacy issue in general as old modules were recycled to newer controls and they needed to work?

    Btw, I hope I write such sensible English that something can be understood by using a translator :)


    • 8088p.jpg

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    • 8088p2.jpg

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