At 04:17 AM 3/2/03 +1100, Ian McLean wrote: >Is it true that the MCLR cannot be used for reset if the LVP fuse is set ? Not true. RTFM - DS30292C pages 7, 123 >Also, is there any benefit to using a reset chip, or possibly a 555 timer in >inverted monostable mode to provide an inverted square pulse of known >length. The datasheet says that MCLR has a filter built in to ignore small >glitches. Every circuit I have seen simply momentarily ties MCLR low >through a reset button. An external reset is useful in a number of circumstances: crappy power supply (noisy or rise time too slow) or where you desire an external watchdog (high reliability applications). >A have a circuit for a 555 timer to be used as a reset chip, published in >ETI Circuits No. 3, Pg. 77. I have SPICE'd this circuit and it seems to do >a good job in simulation. If you are going to use an external reset controller, use something designed for the job. The 555 approach gives you nothing better than what is already on-board the '877 - that design was appropriate for the micros used in that time period but not for modern PICs. Specifically: how does it behave in brownout? Does it maintain reset active all the way down to 0V supply? How does it behave if the power supply comes up very slowly? Finally - search the archives. Even a quick google search on PIC 877 reset controller will most likely provide the answers you are looking for. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 19 years of Engineering Innovation (1984 - 2003) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body