Re: Dead PET 2001 with 6550´er

From: Marko Mäkelä (Marko.Makela_at_HUT.FI)
Date: 2002-04-16 14:44:45

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    On Tue, 16 Apr 2002, Nicolas Welte wrote:
    > It seems the VSYNC signal is also needed for the computer part to
    > start up (IRQ source, IIRC), so this machine also showed the dead
    > machine symptoms.
    True, VSYNC is the source of the periodic system interrupt that reads the
    keyboard and updates TI.  I don't know what other things it could do.  But
    shouldn't the PET display the start-up screen when this IRQ source is
    disabled?  It just wouldn't respond to the keyboard.
    I think that there must have been other problems as well in that machine.
    Maybe the ROM code hung in some place where it polled the state of the
    video circuitry to see when data can be safely written on the screen
    (remember the "smoke poke" discussions a few years ago?).
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