Post by thread:[PIC]: Two PIC16F877 Questions

Hello, Two questions: 1. The PIC16F877 has 2 Vss and 2 Vdd pins. Do both Vss/Vdd pins need to be connected to +5V/GND? Can I supply 5V to one Vdd pin and then get 5V from the other Vdd pin? 2. I am running 3 PIC16F877 in my project. Can I use the same clock for all of them? If so, what are the pro's and con's of doing this? Regards, Donovan -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

At 06:52 PM 14/01/2002 -0800, you wrote: >Hello, > >Two questions: > >1. The PIC16F877 has 2 Vss and 2 Vdd pins. Do both Vss/Vdd pins need to >be connected to +5V/GND? Can I supply 5V to one Vdd pin and then get 5V >from the other Vdd pin? No, you must connect BOTH Vss pins together and BOTH Vdd pins together. >2. I am running 3 PIC16F877 in my project. Can I use the same clock for >all of them? If so, what are the pro's and con's of doing this? Check the archives at http://www.piclist.com for that one. I seem to recall that you *can* but it's messy unless you use a master clock (crystal & 74xx buffers) to drive them all. Using 3 resonators/crystals may be easier/cheaper. Regards... -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

At 06:52 PM 1/14/02 -0800, Donovan Parks wrote: >Hello, > >Two questions: > >1. The PIC16F877 has 2 Vss and 2 Vdd pins. >Do both Vss/Vdd pins need to be connected to +5V/GND? ** YES ** >Can I supply 5V to one Vdd pin and then get 5V from the other Vdd >pin? ** NO ** > >2. I am running 3 PIC16F877 in my project. Can I use the same clock for >all of them? ** YES ** >If so, what are the pro's and con's of doing this? A little more work up front. Essentially, you build the oscillator section as normal for the 1st PIC, then take the OSC out of the 1st PIC and run it into the OSC input of the 2nd. It has worked at low frequencies for many people (4 MHz) but I would be leery about trying it at 20 MHz. You probably need to decrease the crystal loading capacitor on the OSC out pin by the amount of the input capacitance of the 2nd pin (thats the extra work). You may also have EMI and EMC considerations to deal with. Of course, if you use an external clock to supply ALL the PICs, no problem at all. dwayne Dwayne Reid <.....dwaynerKILLspam@spam@planet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

On Mon, Jan 14, 2002 at 06:52:42PM -0800, Donovan Parks wrote: > Hello, A suggestion. It's helpful if you actually wrap your lines... > > Two questions: > > 1. The PIC16F877 has 2 Vss and 2 Vdd pins. Do both Vss/Vdd pins need to be > connected to +5V/GND? Yes. On larger chips there can be multiple Vcc/Vss pins to route power to different areas of the chip. Unless the data sheet gives specific instructions about their usage, you must supply +5/GND to each power in. > Can I supply 5V to one Vdd pin and then get 5V from the other Vdd pin? NO! (emphatic double hands/STOP gesture!) Each and every Vdd needs to be connected directly to the power supply. > > 2. I am running 3 PIC16F877 in my project. Can I use the same clock for all > of them? As long as the runs are not too long and you use an oscialltor > If so, what are the pro's and con's of doing this? Neither if you do what I outlined above. BAJ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Isn't the OSC out actually OSC/4? That's just off the top of my head though... Josh {Quote hidden}> >2. I am running 3 PIC16F877 in my project. Can I use the same clock for > >all of them? ** YES ** > >If so, what are the pro's and con's of doing this? > > A little more work up front. Essentially, you build the oscillator section > as normal for the 1st PIC, then take the OSC out of the 1st PIC and run it > into the OSC input of the 2nd. It has worked at low frequencies for many > people (4 MHz) but I would be leery about trying it at 20 MHz. You > probably need to decrease the crystal loading capacitor on the OSC out pin > by the amount of the input capacitance of the 2nd pin (thats the extra > work). You may also have EMI and EMC considerations to deal with. > > Of course, if you use an external clock to supply ALL the PICs, no problem > at all. > > dwayne -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

Josh Koffman wrote: > > >2. I am running 3 PIC16F877 in my project. Can I use the same clock for > > >all of them? ** YES ** > > >If so, what are the pro's and con's of doing this? > > > > Of course, if you use an external clock to supply ALL the PICs, no problem > > at all. Search the net for a "one transistor crystal oscillator", they are very simple and have plenty of output power to drive a few PICs from the one crystal. -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads