16F877A vs 16F877 reliability

Eugeneo · Joined: 30 Aug 2005 Posts: 155 Location: Calgary, AB

For one of my older projects I decied to use a 16F877A since the chips were cheaper in quantity.

Bad mistake. It works but the reliability is gone.

I've checked the updated specs for the osc. caps and startup but I still can't get it to function as solid as the non 877A chip.

I've compiled and re-programmed with the 877A specs.
It says it's not necessary to turn of the comparitor since it is off on powerup.

Still I swap chips and the 877 never fails. The 877A trips the WDT an average of once every 2 hours.

Any suggestions? Have I missed something?

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

I have not seen this. I have a new product. with 6 prototype boards made, with the 877A. I will enable wdt and put in a restart_cause() statment. I'll run it for a few days and see what happens. Perhaps you got bad silicon.

d00dajo · Joined: 20 Jul 2004 Posts: 34

Eugeneo:

The biggest difference between 877A and 877 is that the pathways inside the silicon have been greatly reduced. There are indeed a number of reliability issues related to the A version. Are you using A/D measurement in your application? If so, it is not necc. the watchdog that restarts the cpu (Restart_cause() is not always reliable).

You could test disabling the BrownOutReset circuit. If you no longer get the random resets, I can give you some hints on what the problem / workaround might be with the 877A.

//Daniel Johansson,
Sr. Application Engineer, EmpirBus AB.