Date   : Sat, 11 Feb 2006 20:39:13 -0000
From   : "David Harper" <dl.harper@...>
Subject: Re: B+ 64k won't respond to keyboard, Econet fitted

"neil f" <faz@...> wrote:

> When I press Break, the "32K" disappears from the title. Crtl/Break
> restores it. Delete/Break changes file system as normal according to
> the title message. So it seems Break+key combinations are recognised
> and acted on correctly, but no other keypresses get any response on
> screen. I'm loath to start clipping the legs off the 6522 chips to
> unsolder and replace them, but maybe that's the only option left. I've
> substituted keyboards and cables and run with no ROMs at all other
> than OS but the result never varies: the ">_" prompt just sits there
> waiting with the underline flashing as normal.

This means the Ctrl and Delete keys are both being recognised correctly. The 
interfacing with the keyboard must be working (so don't remove the 6522 
yet!).

The keypresses are detectable, but it seems that nothing is being entered 
into the keyboard buffer. That sounds to me like a failure of interrupts. 
Either keypress interrupts are not being caused, or else they are not 
getting through to the CPU.

It cannot be the 6502 (CPU) itself, because otherwise the cursor would not 
flash. (That happens on the VSync interrupt generated by the 6845, so these 
must be being detected OK.)

It might still be the 6522 VIA, which could be failing to generate the 
appropriate interrupts, but I suspect a more likely culprit is a broken 
motherboard track.

David Harper