Hi Dwayne, I have an experience with 16f parts that some functions not working. But when I reprogrammed the chip it becomes perfect working condition. I had enabled Brown out reset. The question_ How the code altered from program memory is still confusing me. But this condition is a rare problem to me now. But I believe if it occurred once it will be a problem soon or later. On Fri, Dec 14, 2012 at 11:11 AM, Xiaofan Chen wrote: > On Fri, Dec 14, 2012 at 7:17 AM, Dwayne Reid > wrote: > > Part of my problem is that I simply have NOT yet done any > > hazardous-location projects without including an external > > watchdog. Most of those past projects involve copious amounts of > > Natural Gas (the largest ovens that we have done run at 30 million > > BTUs) and I simply won't do a controller that doesn't have redundant > > watchdogs. But that limits my experience with modern PICs, simply > > because most projects DO have watchdogs. > > Actually my first project with PIC is for the hazardous (Zone 2, > Class 1 Div 2, EEx ia, intrinsic safety isolated barriers) using > 16C72A and without external watchdog or power monitor IC. > On the other hand, I do make sure the internal power supply > guarantee the spec of the PIC power requirment. The product > family have been running in the field (mostly oil and gas industry) > for more than 10 years and the run rate is about 100k to 200k > pcs per year. It has also SIL 2 (Functional Safety) certification. > > I have also used the 16F872A in the other hazardous location > application (Zone 0, Class 1 Div 1, NAMUR sensor) with external > reset circuitry. It needs to run at very low current to fulfill > the NAMUR sensor standard. Again the product have been > out in the field for quite a few year and run fine. > > So it depends on the application. Usually the MCU failure > will not cause hazardous conditions since it is not a safety > component anyway and the other circuits will protect against > the hazardous conditions (eg: limited U, I, L and C in the case > of Intrinsic Safety). > > > I'm willing to take a chance with these tiny heaters because a > > failure won't cause a hazardous situation (the extra hardware > > over-temperature cutout protects against this) - a failure would just > > cause customers to be unhappy with us. But if anyone can tell me > > that they did something to make one of these newer PICs to lock up or > > hang, I would very much like to hear about it so that I can try to > > duplicate the situation here. > > > > Moving to a small PIC lets me to reduce the BOM cost by a few percent > > and allows me to do some neat things that the current all-analog > > design can't do. But I don't want to jeopardize reliability by > > making the change. > > The current product we produce are not as stringent in terms of > hazardous application but we make it a rule to use external > power monitoring circuitry and watchdog (to shutdown the output > in case the MCU hang). > > > -- > Xiaofan > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .