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Thread: VT82C42N keyboard controller generating continuous interrupts

  1. #1

    Default VT82C42N keyboard controller generating continuous interrupts

    I'm using a VT82C42N keyboard controller for an 8088 computer I'm building, but it generates continuous interrupts. I removed the instruction that sends AAh to the controller, but it still generates infinite interrupts. I programmed the ISR to print the hexadecimal byte that's put on the data bus and it's FFh.

    I wired it up to work in PS/2 mode. I hooked up P26 to a 74LS04 inverter since I don't have any 06s (I'm not sure why the schematics say 06s), and the resulting signal (Keyboard clock) goes to the keyboard and TEST0. P27 goes to an inverter and the resulting signal is Keyboard Data, which goes to the keyboard and P10. I'm confused at this setup, but that's what the datasheet says to do. I don't know why the output signals from the keyboard would be hooked up to an output on the inverter. I wonder if this is generating continuous 1s to fill up the shift register in the serial port of the VT82C42N.

    http://pdf1.alldatasheet.com/datashe...C/VT82C42.html

    I've seen that a few people on here have used this chip before, so I figured they might know what's going on.

    Edit: I should mention that I hooked up P24 to an LED to confirm it wasn't a problem with my PIC, and sure enough, P24 was high.
    Last edited by otacon14112; July 9th, 2017 at 07:21 PM.

  2. #2
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    Quote Originally Posted by otacon14112 View Post
    I wired it up to work in PS/2 mode. I hooked up P26 to a 74LS04 inverter since I don't have any 06s (I'm not sure why the schematics say 06s), and the resulting signal (Keyboard clock) goes to the keyboard and TEST0.
    The 74LS06 has an Open Collector output. The 74LS04 does not. That is an important difference. They are not interchangeable.

    If you don't know why the design uses Open Collector outputs you need to think about it a bit more.

  3. #3

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    Ok, well I was going to order some 06s, but I read that they were interchangeable, so that's why I used the 04 instead. Guess I'll order them anyway. Thank you, btw.
    Last edited by otacon14112; July 10th, 2017 at 09:31 AM.

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