Is it just me, or is the message below missing line breaks? " I just has a horrible thought about this. The most likley way to screw i= t = up would be to simply enable the UART transmitter on all the slave pics. = Then you would have say 5 idling high and one pulling low. " Did you not get my message about using an OC driver? Vitaliy ----- Original Message ----- = From: "Colin Constant" To: Sent: Wednesday, January 28, 2009 12:19 Subject: RE: [PIC] Do I need a transceiver? > > I'm setting an async network with multiple PIC 16F690s and 16F886s.> > = > > One master and 6 of 8 slaves spread over a distance of maybe 6 feet.> >= > = > > > The slave Tx lines all talk to the master Rx. I'm worried about the>= > = > > case where one slave tries to pull the line low while another pulls> > = > > it high. I was thinking maybe a 10K pullup on the mastter Rx and a> > = > > diode pointing to each slave Tx.> > That's going to be slow. A collisio= n = > > should never happen during normal> operation since that would be a = > > firmware bug. That means you only need to> protect the hardware to the = > > point its max rating isn't exceeded. If a> collision happens, something = > > else at a higher level has already screwed up,> so there isn't anything = > > you can do at the low level to fix the problem. The> only objective is = > > to make sure nothing blows up.> > PIC pins are rated for 25mA. Put 120 = > > ohm resistors in series with each> slave transmit line. If two PICs = > > drive opposite directions you get 5V / 240> ohms =3D 21mA. Not great, b= ut = > > within spec, and 120ohms should still allow for> reasonably fast data = > > rate. You should also put a resistor in series with> the incoming line = > > followed by reverse Schottky diodes to power and ground.> I just has a = > > horrible thought about this. The most likley way to screw it up would = > > be to simply enable the UART transmitter on all the slave pics. Then = > > you would have say 5 idling high and one pulling low. _________________________________________________________________ The new Windows Live Messenger. You don=92t want to miss this. http://www.microsoft.com/windows/windowslive/messenger.aspx -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist = -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist