Hi. I bought the CPLD kit and have been working thru the tutorials. It has been a great experience.
I am having problems with the 7555 clock being detected or maybe processed by the CPLD. I have a scope on the clock output and can see it generates consistent clocking, but the output pins are missing counts (e.g. they literally are skipped). For example, in lesson 7 which is currently setup, the LED will cycle thru something like 1,2,3,5,6,7,9 (and this is not consistent).
I discovered if I feed the clock from a function generator, no problem. The only difference I see is the function generator provides 3.6v and the 7555 is providing 3.28v.
I created a separate 7555 running on 5V and fed it's clock to the CPLD. That works 100% correct. I then used a fixed 3.3v power supply that produces about 3.4v and it works nearly correctly on that - dropping only the 0.
You don't have any problem on your videos. I've checked the code and wiring repeatedly and see no problems there.
I'm baffled.
Dan
7555 Clock Issue in Lesson 6 and 7
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Re: 7555 Clock Issue in Lesson 6 and 7
ricochet82 wrote:Hi. I bought the CPLD kit and have been working thru the tutorials. It has been a great experience.
I am having problems with the 7555 clock being detected or maybe processed by the CPLD. I have a scope on the clock output and can see it generates consistent clocking, but the output pins are missing counts (e.g. they literally are skipped). For example, in lesson 7 which is currently setup, the LED will cycle thru something like 1,2,3,5,6,7,9 (and this is not consistent).
I discovered if I feed the clock from a function generator, no problem. The only difference I see is the function generator provides 3.6v and the 7555 is providing 3.28v.
I created a separate 7555 running on 5V and fed it's clock to the CPLD. That works 100% correct. I then used a fixed 3.3v power supply that produces about 3.4v and it works nearly correctly on that - dropping only the 0.
You don't have any problem on your videos. I've checked the code and wiring repeatedly and see no problems there.
I'm baffled.
Dan
I know we e-mailed back and forth a few times. I wonder if you ever figured out the issue here.
Seems to be a very, very odd bug.
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Re: 7555 Clock Issue in Lesson 6 and 7
Never did figure it out. Every lesson required 5V on the clock pin to work. I used different CPLDs, 555 timers, power supplies, etc. Completely bizzare. But I've moved on to a MAX II with an onboard clock now.
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Re: 7555 Clock Issue in Lesson 6 and 7
ricochet82 wrote:Never did figure it out. Every lesson required 5V on the clock pin to work. I used different CPLDs, 555 timers, power supplies, etc. Completely bizzare. But I've moved on to a MAX II with an onboard clock now.
Sorry I couldn't give you a better answer. I used many different 7555 countless times as a clock both fast and slow and could never reproduce what you saw.
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Re: 7555 Clock Issue in Lesson 6 and 7
Last edited by Ayan Prince on Tue Dec 22, 2015 12:55 pm, edited 2 times in total.
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Re: 7555 Clock Issue in Lesson 6 and 7
I did not. I moved to an Altera MaxII and never experienced any problems with it.
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Re: 7555 Clock Issue in Lesson 6 and 7
ricochet82 wrote:I did not. I moved to an Altera MaxII and never experienced any problems with it.
Glad to hear it worked. Moving to newer technology might have helped as well

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