At 09:23 PM 3/17/02 -0800, John Dammeyer wrote: >Hi all, > >I'm just laying out a board with a 16C877 on it and I've included the RJ >connector so I can use the PIC-ICD for programming and debugging. I've >got a couple of MCP2510 CAN devices all attached to the MCLR line for a >common reset. As I started the layout I realized that the programming >voltage used to put the device into High Voltage Program mode would be >passed onto the other devices. I use a small diode (1n4148) between the PIC and the rest of the devices: K to MCLR, A to other devices. Needs 2 pullup resistors - one on each side of the diode. Put your reset controller right at MCLR; make sure it can handle Vpp without damage. Asserting MCLR (pulling it LO) will pull the !reset line of the other devices LO via the diode. I use this technique on several of my controller boards: it allows ICSP without damaging the shift registers who's !reset lines are also controlled by the watchdog/reset controller on the board and it also allows some of those !reset lines to have a simple monostable timer on them (keep the SRs held in reset if the watchdog keeps resetting the PIC). The only caveat is to make sure the forward drop of the diode does exceed the maximum allowed voltage to be regarded as a logic LO. That is not a problem for the SRs that I use and should not be a problem for the MCP2510s - but check it! dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' 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 hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads