[Coco] Coco Digest, Vol 155, Issue 42

[Barry Nelson]

 Like Darren A said below the state of the SCS line is undefined except when E is high, even during relatively brief times when you would not expect it. It is suggested that you always check E=HIGH before reading the SCS line, otherwise you may get strange unexpected results when you least expect it.
> Well that may be what's happening with the games.  For my purposes I still think the SCS alone should be enough for what I'm wanting to accomplish.  As I said, the SCS status will be ignored at all times EXCEPT when a .BIN has just been loaded.  Once the .BIN load has been completed, the SCS will again be ignored.   There's no reason for the SCS to be triggered for any reason from power-up during the .BIN loading process EXCEPT by the assembly loader signaling the end of the 8K segment.
> 
> - Chad H
> http://sites.google.com/site/cbhlab101/
> 
> 
> -----Original Message-----
> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Darren A
> Sent: Saturday, October 17, 2015 8:48 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] SCS Line (or others?) - Atmega Microcontroller monitoring
> 
> On Sat, Oct 17, 2015 at 7:01 PM, Chad H wrote:
> 
> > P.S.  I'm observing already that several of my ROM/BIN games seem to 
> > be triggering the SCS a lot while running.  I thought it might be 
> > games that use joysticks but Color Baseball doesn't trigger any SCS events, neither
> > does 8-Ball.   I was already going to have my controller ignore SCS events
> > except for when it's loading .BIN segments, so this won't be a problem.
> > Just curious is all.
> >
> > games already seen to trigger the SCS line include..
> >
> > Atom (Still don't know how to play this one) - my SCS trigger 
> > increment counter is going slow and steady on this one.
> > Downland - Its running pretty fast on this one.
> >
> 
> 
> 
> You should not rely on SCS alone. It should be gated with the E clock and only recognized as a valid access when SCS is low and E is high.  False triggers of SCS can occur while E is low and the address bus is transitioning.