On Tue, Feb 27, 2007 at 09:57:00AM -0500, Jeff Findley wrote: > > "Wouter van Ooijen" wrote in message > news:033801c75976$03821c20$0b00a8c0@PAARD... > >> And similar descriptions apply for U2 to U1 transmissions. > > > > But how do you resolve when both sides attempt to transmit at the same > > time? > > That's the problem with only using two lines and also requiring "no timing > and no interrupts", isn't it? Actually I think it's an orthogonal problem. > If you could use some sort of timing, you > could require all transmissions to start with the same bit and you could > time-out if you don't get an acknowledge after a certain period of time. But timing is out. > Then you still need to come up with a way to make sure the two pics don't > immediately try to talk at the same time again. Again I think it's an orthogonal problem. It's a multi-master issue, not a timing issue. A upper level protocol that using polling would resolve this problem because then there would only be one master in the system. What isn't resolved is when only one working system is on the line. I think there has to be some sort of timeout, even if it's an extraordinarily long one (like 2-3 seconds) BAJ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist