8086, ALE never goes high

Discussion in 'Embedded Systems and Microcontrollers' started by slagment, Jul 30, 2009.

  1. slagment

    Thread Starter New Member

    Jun 29, 2009
    Hello to any 8086 experts,

    Basically I just want to see some signs of life from my board, but all I get is garbage from the address and data lines. Which means somewhere I have entered garbage.

    I noticed that ALE never goes high, which makes my think I have a physical problem, improper design or mis-wire.

    Please, any ideas why ALE line is low? Attached is a snap-shot of my logic analyzer going off the ~5Mhz clk, code, and schematic file.

    Thank you
  2. RiJoRI

    Well-Known Member

    Aug 15, 2007
    (1) Are the oscillator inputs working? (Probably something like XTAL1 & XTAL2.) Do you have an oscilloscope? This will help a lot more. No clocks => no operation.

    (2) Isolate the ALE, and see if it is operating. If not, you may have a bad chip.

  3. slagment

    Thread Starter New Member

    Jun 29, 2009
    I checked the CLK input and its running just below 5MHZ.

    I checked the ALE with the logic analyzer over several resets, it stays low.

    The chip was manufactured in 1976, think I'll order another.

    Thanks, keep the ideas coming.

    *I re-order all the basics to at least see the reset address, 8086, osc, clock chip.
    Last edited: Aug 1, 2009
  4. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    anytime I have put together a system that doesn't perform, I'll add a timed reset circuit that runs off the system clock. If you configure it such that your system is reset every 20 clock cycles to start with, then you can scope your lines to see if how your system comes up from reset. So you would check that your reset vector is being fetched with appropriate control signals as well as status signals, that the code being fetched is as expected, etc.
  5. slagment

    Thread Starter New Member

    Jun 29, 2009
    I like that idea too.

    Also, my reset switch could be the problem. It's simple enough to rebuild and check.