myke predko wrote: > What type of capacitors have you put on your crystal? Along with that, what > type of crystal are you using (should be parallel cut). > > Have you 'scoped/checked the OSC1/OSC2 lines? OK, I assumed that since my LCD was printing characters all right the clock was OK. However, I see that I have oscillation on OSC2 but not OSC1. I am using 33pF capacitors from the oscillator pins to ground but I don't know if my crystal is parallel cut. (Its marking is 4.000 UNT 97-HX but it was bought over the counter in a shop from a clerk who can't tell the difference just like me). > > I suspect that when you went to a different board, the capacitance built in > your prototyping system was missing and that doesn't allow the crystal to > start oscillating. Actually, the programmer/prototype board is a nice double sided professional job and the only parts on the protoboard are the zero crossing detector (using a LM393 comparator) and the LCD. > For 4 MHz, use a couple of 33 pF capacitors connected from OSC1 and OSC2 to > ground. > > myke Thank-you for taking the time to look over this problem! Bruce > ----- Original Message ----- > From: "Bruce Douglas" > To: > Sent: Monday, September 02, 2002 12:52 PM > Subject: [PIC]: Problem with 16f877 > > > >>I have a project which is a binary FM code reader made with a >>877. This decoder uses both upward and downward transitions >>and times them. 2 short transitions are a 0 and one long >>transition is a 1. I am using RB7 with an Interrupt on Change >>to capture the transitions. >> >> >>The problem is that this code is working well in one of those >>project boards (a programmer together with LCD, pushbuttons >>and LEDs). When I put the same PIC into a dedicated >>PCB, it won't read the code. The connections seem to be OK >>since it writes to the LCD and there is a nice 0-5v square >>wave coming into RB7. >> >>- All ports are programmed as outputs except for RB7, >>- An LCD on RB1 to RB6 works fine >>- there is a decoupling capacitor right on the power input pins, >>- MCLR is connected to Vdd, >>- the oscillator is a 4Mhz cristal. >> >>Are there any other gotchas that need to be taken into account? >> >>I am assuming that this has to be a hardware problem since I >>take the same chip that works in the prototype board (and works) >>and put it in the PCB (and it turns on the LCD at 00 and won't >>count up). I have appended my initialization code, anyway. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body