Re: Fat40 RAM problem?

Hi Istvan,

Sorry for the late answer. 

On Monday 01 September 2014 14:29:00 Istvan Hegedus wrote:
> > Hi,
> 
> Just a quick question regarding the scope picture. I am new to oscilloscopes
> and have one Gwinstek, similar to this Rigol.
> I can measure periodic signals well but have problems setting triggering for
> these logical signals.
> How do you set trigger so that you can capture a certain event on these
> digital lines?
> 
To get a good signal, you have multiple options:

1) Use a periodic "trigger". In my case I had a BASIC program running that was 
periodically writing to the memory location. As this particular RAM chip was 
only used for this POKE (it was the upper 16k that was broken and not the 
lower 16k which was used by BASIC) it was easy - just use the /CAS signal on 
the RAM chip as trigger input. The BASIC program triggers it periodically, and 
nothing else, so that's easy.

2) if it would have been the lower 16 RAM, I would have run into problems with 
that approach. I would have probably tried to write a small machine language 
program that triggers a unique signal (like in the first approach, some I/O 
line, or maybe even the same /CAS signal as above) and immediately after that 
access to the other memory location (or do whatever you want to measure) - you 
can then count the cycles to see where the access is after the trigger and 
check there.

3) If that is not easily done, many scopes have a "one shot" mode. You use a 
signal for trigger and the scope just records the first occurrence, no matter 
if that signal triggers again after the first time. 

4) sometimes, if nothing else helps, you could build a small circuit that 
creates a trigger for you. Like combining some logic signals, or counting 
triggers, and, say, trigger on the Nth occurrence only

 Hope this helps
André


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