[Opendispense] Latest additions

Bernard Blackham dagobah@ucc.gu.uwa.edu.au
Sun Aug 3 17:05:10 2003


On Sun, Aug 03, 2003 at 10:32:51PM +0800, Harry McNally wrote:
> > There's also another circuit attached to PE3 which puts the pin high if
> > the 24VUN (unregulated?) drops below 20ish volts. Still tracking down
> > where they're used. I think I'm currently on a roll with the coin mech :)
> 
> I think this may sense that mains power has been lost. The switch
> mode regulator that provides 5 volts will hold up for a while as the
> 24VUN collapses so the micro may have time to finish any nonvolatile
> RAM writes and maintain system sanity for when power returns. I
> was chatting to Nick about using that for our own system preservation
> on power fail.

The only reference I can find to the PE3 pin with this circuitry on it
is in the following snippet of assembly in the main loop, which it seems
holds the reset line of the changer high until 24V power is restored.

Perhaps it's a power-saving technique? Or stops the changer from
dropping out coins just because the powers flaky? (the corresponding
lines are active low). Or I could just be way off track altogether :)

Baffled and sleepy but making more progress.

Bernard.