This has proved to be a major headache for me on designs which won't work without an MCLR cap. I had a jumper to the cap that I could remove for programming, and that worked for development. one could also try a resistor-cap-resistor to allow the fast risetime at the pin but still filter transients from the power supply or from EMI. It is not just the ICD2 that has this problem - all of the ICSP programmers I have tried also wheeze when a cap is connected to ground from MCLR. FOr most development projects you can dispense with the cap but it is handy in the real world. -- Lawrence Lile Ken Pergola Sent by: pic microcontroller discussion list 12/10/2003 11:41 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [PIC]: Best pullup resistor value for /MCLR pin? Mike Hord wrote: > IIRC, the ICD2 manual discourages this practice because it can affect > the timing with which the line is brought to Vpp. Good point, and yup, you definitely recalled correctly Mike. Anyone designing for ICSP should definitely read the programming specs for the device they are using since some (not all) of the programming specs on the PIC18F, for example, call out a *maximum* of 1 uS rise time on MCLR/VPP to enter Program/Verify mode. Depending on the output impedance of your VPP source, it won't take much capacitance to violate this spec. Best regards, Ken Pergola -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.