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Digital Logic Common Faults

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haroldbrown

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This is what i have come across when troubleshooting digital logic TTL or CMOS circuit

input and output stuck high or low
input or output shorted to VCC or ground
Data line stuck high or low
Address line stuck high or low
Clock signal is stuck high or low or not working
Noisy logic signals causing false triggering
logic chips not advancing to the next cycle or returning
Logic chips not resetting

Can you add to the list?
 
Are you Walters, back again? Same kind of name as the other names you used here and on other forums (Billymayo, Dannydavis, Prescottdan, Davewalker, Castillovan and Vancastillo).
Electronic circuits are so reliable that they rarely fail today if they are designed properly and conservatively. If a consumer product fails then the product is thrown away and replaced, not repaired.
I think those old circuits for old airplanes should be thrown away and replaced. Maybe you should also be replaced.
 
Aw... don't be a spoil sport AG.
There was me about to add:

Top blown off the chip due to passing too much current.

JimB
 
Use whiff test for remnants of magic smoke. Same goes for BS...
 
When you have logic reading problems, it's mostly EEPROM chips or what else can cause logic reading problems?
When you have logic writing problems, it's mostly RAM chips or registers chips that is causing the logic writing problems?

Thanks for the help
 
Are you Walters, back again? Same kind of name as the other names you used here and on other forums (Billymayo, Dannydavis, Prescottdan, Davewalker, Castillovan and Vancastillo).
Electronic circuits are so reliable that they rarely fail today if they are designed properly and conservatively. If a consumer product fails then the product is thrown away and replaced, not repaired.
I think those old circuits for old airplanes should be thrown away and replaced. Maybe you should also be replaced.
IP certainly fits.....
 
I'ts been close to 20 years since I last saw a commercial product which uses discrete logic in lieu of complex programmable devices, like microcontrollers or FPGAs.

When using said programmable devices, the "failures" I've seen are related to software bugs which can be as simple as an incorrect fuse selection or complex as improper interrupt handling.
There are other obscure failures like incompatible brownout levels and/or not implementing an effective watchdog strategy.

When hard failures do occur, sometimes are stuck output ports, or input ports that fail to respond to the stimulus. But in many instances, those failures are not exclusively related to the port itself, but to circuits buried deep within the silicon.
 
incorrect fuse selection

Each Microprocessor software program has a different list of "soft fuses". I have seen designers use the same microprocessor but use different software programs because the soft fuses had different functions and options. I don't understand why different microprocessor software programs use different fuses and why not all use the same. The software programs would load a bootloader hex file first and then a firmware hex file. I'm not sure what these soft fuses do to the microcontroller.

When loading the firmware hex file the microcontrollers bootloader program would be on a timer looking for a firmware, if it doesn't find a firmware in 10seconds it would default to the bootloader. I'm not sure what this timer is called when the bootloader program is looking for a firmware.
 
Microcontroller Test Points
1.) Check the crystal oscillator waveform and timing
2.) Check the ALE output signal which is the ALE address latch enable output
3.) Check the PSEN output signal wich is the Program store enable output
4.) Check the Watchdog circuit
5.) Check the Interrupt input

I have to disable the watchdog circuit when i get a stuck high or low logic state on a date line or address line
 
Leakage current excessive from ESD wounds, or back EMF pulse
Almost opens
almost shorts.. From overstress
High ESR on output
Race conditions (metastable)
Latchup condition (temporary fault from input or output exceeding Vcc or ground by 0.5V
Speed error, latency rise time setup

Etcetera

Crater on CPU from fan fail, overclocked, no heatsink
Internal state flaw
And lots more

Dont forget design flaws, thats the biggest problem....next to solder flaws
 
I forgot about the asynchronous metastable error that only happens only when hot or Murphy is around. Reminds me of an HP card that always worked when debugging on a card extender until I put a soldering tip on it for a few seconds.
 
...if it doesn't find a firmware in 10seconds it would default to the bootloader. I'm not sure what this timer is called...
Suspected from the beginning, but this definitely gave him away. The pressure of having names for everything is just.. unique.
 
Soft Fuses might be some form of patent protection, which in itself must be unique for each company to not violate a patent.

Hard fuses protect IP content of Fusemask ROM from being read. Hard Fuses are no longer patent protected.

Are you thinking of Flash Memory or write once ROM with fuselink
 
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