At 05:01 PM 8/15/97 -0400, you wrote: >On Fri, 15 Aug 1997 14:12:41 -0500 Lynn Richardson >writes: >>One thing to watch with PICs is brownout situations. They don't seem >>to have a true power on reset like others. You have to be sure if VDD >>goes below 2V it and all other IO pins continue to go down to VSS before >>VDD comes back up. If you don't, there's a chance the IO ports will have >>pins latched into a high or low output and no way to overide by >>resetting the TRISx register or port register in your program. >> > >I've noticed this too, on an F84. The pins do strange things like >driving high but not low. Also, the program doesn't run properly. This >was just in the process of turning the power on for the first time, using >a circuit with a transformer, rectifier, filter, and 7805. Pulling the >MCLR pin low does not help. It is necessary to jig the power up and down >until it starts properly. Not good at all. Apparently there is some >sequential stuff in a PIC that MCLR doesn't clear. I've only seen it on >one chip (set the project aside for other reasons before trying any >others) but I don't think there's anything wrong with the chip because >once it starts it runs properly. > It's actually much worse that that. If the part includes EEPROM, there is a good possibility that the EEPROM will be written. I know that it happens with 16F84's and I've been informed by another user that it happened on his product that uses 16C84's. It would seem some type of brown-out protection is mandatory for those parts with EEPROM on board. My product is through-hole, so I'm using the Dallas DS1233D. I've seen the Maxim part mentioned on this list several times. By the by, on my product the watchdog would not reset the part after brownout even though it was enabled. It makes me wonder what its for... Regards, Jim Jim Ham, Porcine Associates (415)326-2669 fax(415)326-1071 "http://www.porcine.com"