But RB4 wouldn't pull low until the program starts - or was it an external pulldown? RP It was tied directly to RB4 that was pulled low to avoid entering programming mode. (Because I didn't need it as an input and the figure in the programming reference stated taht to enter LVP MCLR and RB4 would rise to VDD together...) This turned out to prevet the circuit from ever starting... very wierd... Kyrre ----- Original Message ----- From: "Olin Lathrop" To: Sent: Thursday, November 07, 2002 11:22 PM Subject: Re: [PIC]: Wierd thing about the 16F628 ??? > > There was something wierd the orther day about my 16F628 based > prototype... > > I could simply not get the thing to execute code! > > After going through all the docs again I still hadn't found what was > wrong > > so I did something that shouldn't have solved the issue according to > specs. > > I tied MCLR to VDD *even* if it was already tied to VDD internally. > (Yes, I > > had disabled it because I didn't need it, and I was using LVP ICSP.) > > Now, everything worked as it was supposed to? > > What were you doing with MCLR before tying it to Vdd, floating? If so, > that could easly be the problem. MCLR is a CMOS input, which should never > be left floating. Any stray noise or static electricity could drive it in > any direction. Disabling master clear internally only keeps a low level > on the MCLR pin from causing a reset. It doesn't mean the MCLR pin is > driven low (if it was, it would still be useless as an input). Since MCLR > has no protection diode to Vdd, it could have picked up noise and driven > the chip in to high voltage programming mode. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu