Thanks Guys! First, sorry for the insufficent info. RB0-7 are set as output. But only RB4-7 are used. Assume all un-used port as default value on POR. Will this likely to cause this problem? Will attempt to set all usused port to output. Secondly, would like to know clearing bit 7 (LVP) of configuration word do the job or setting the Config Bits in PICSTART Plus in Programming mode? God Bless ALL PICers! Best Regards, Tee ----- Original Message ----- From: Alan B. Pearce To: Sent: Tuesday, March 20, 2001 4:32 PM Subject: Re: [PIC] 16F877 works only when pulldown to ground with resistor > > Subject: [PIC] 16F877 works only when pulldown to ground with resistor > > > > Hi, > > Do any kind soul have any ideal why my 16F877 work only when I pulldown all > un-used port to ground? > > I used a 10k resistors to do that. Both VDD & VSS are connected and Pin 1 to > reset. Chip running at 4Mhz. > > I thought someone else would have mentioned it, but if you have Low Voltage > programming turned on, then RB3 has to be held low for the chip to operate. If > it is not low then you are in program mode. > > -- > 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.