On 5/4/07, wouter van ooijen wrote: > > The resistor pulls up the MCLR pin when the ICSP programmer is > > disconnected. If it were only being driven by the ICSP, disconnecting > > the programmer would leave the pin floating. > > But connecting the R to Vcc gives a problem: current into Vcc which > might raise Vcc. Why not connect that R to ground, and make it realy > high? (let's say 220k). Wouter, One of the problems which I'm naming " PIC folklore" is the "raising Vcc". The Vcc is generated from a regulator. Any regulator has a negative feedback. Any regulator is generating the voltage on a load, it has nonsense to keep a regulator output unloaded. As long the negative feedback is linear comparing a fraction of the output voltage with the internal reference voltage, any raise of the output voltage is compensated, so the output voltage will be lowed to the nominal regulator value by the series transistor inside the regulator. The over voltage will be absorbed by the load. What is missing from PIC users is changing the LM7805 at least for one day with the LM723. In this way that raising problem will be completely understood and also the complete analyses of the feedback. The same situation it's visible on the switching supplies or parallel configurations of any linear supply. Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist