----- Original Message ----- From: "Spehro Pefhany" To: Sent: Friday, July 30, 2004 11:15 AM Subject: Re: [OT] high temp (>85C) microcontrollers You may run into issues with other parts on the board as well if you're pushing 1000C actual operating temperature. Both with performance and with especially with life. Most characteristics of parts are poorer at very high (and sometimes at very low) temperatures, so careful design is called for. Capacitors, optos, and other parts.. assuming you want the product to last longer than 6 months or a year of continuous operation. The "E" versions of Microchip parts are specified at 1250C, however they will be more expensive and harder to find than the 850C versions. Since they are all the same chip (just tested to different specs) from all manufacturers, the fact you are actually seeing problems may be significant. A PIC16F87xE should do the trick functionally... Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Yes, the other parts are an issue however they were all rated (or de-rated in the case of capactiors and such) for operation at >85C. The continuous operating ambient temp is supposed to be 80C but under some conditions (and a bit too frequently for my happiness) it gets over >100C due to chassis changes. I have on the re-design list to add an additional temperature sensor to monitor the controller and give it an early warning that the ambient temperature is rising above 85C so the system can attempt to modulate the temperature a bit. What seems to be happening with the 'HC705 is that its clock circuit gives up and the part just stops running. The xtal is rated for 125C and a little testing showed me the caps were OK too. I found the "E" versions (I should have said that before) in the datasheets but finding the actual parts is another story. There is a noticable frequency change but because the system is phase locked to the 60Hz line frequency, a little drifting of the xtal frequency doesn't affect operation (no RS232, basically just timing the firing angle of triacs and monitoring some sensors). My first choice would be the 16F877E as a replacement. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads