RE: OT - limitation of PC's parallel port (was: Logic analyzer)
Date: 2002-04-18 08:53:42

  • Next message: "RE: OT - limitation of PC's parallel port (was: Logic analyzer)"
    Hallo Spiro,
    > This analyzer is even mentioned in my diploma thesis.
    I actually build one for mine in 1986/7 :) In fact, yesterday I digged it up
    out of all the rubble I collected in years. It worked on the day I had to
    show it for my thesis and the day after it stopped, mostlikely to the way
    how I wired it. 
    The design was 40 bits but could be upgraded to 64 bits. Why 40 bits? Goal:
    20 addressbits, 8 databits and many controllines of the 8088 PC. It used 5
    2K*8 SRAMs of 100 ns. So 4.77 MHz was doable. 
    The design was clocked by an internal or external clock (like PHI2 of a
    You could program what bits to use as trigger and on what slope. 
    Last feature: the trigger could be used to start sampling 2048 samples, stop
    sampling, or to sample just another 1024 samples.
    AFAIk I still have the original ML program for the C64. The program for the
    PC was lost due to very first virus I ever run into :(
    In fact I have thought about reviving it again two times and started to make
    electronic schematics of the paper ones. I'll have a look for them.
    > Does anyone know what is the (most) limitating factor when 
    > using the PC's parallel port? Is it the usage of I/O
    > address space, or the usage of the ISA bus?
    IIRC we had this discussion about a year (?) ago. (no offence)
    It is the usage of I/O space. When accessing I/O, the CPU is slowed down in
    such a way that you only can do about 500K I/O opereations per second. 
    > I could obtain a PCI card for testing, .....
    I don't have a PCI LPT-card as they are much to expensive :( 
    But I did some projects in the past where I used some memory mapped I/O. The
    only limitation you then have is the limitation of the ISA-bus. Normally 8
    MHz but I used a motherbord where you could configure this speed up to 12
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      / /  |_/     Groetjes, Ruud
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