Dave VanHorn wrote: > I wrote: > > If the transmit clock on the modem is 0.158% faster than the transmit > > clock on the MAX3100, this is exactly the sort of symptom you'd see. > > For every 632 bytes transmitted by the modem to the PIC, the MAX3100 > > is only managing to transmit 631 of them, and one gets dropped. > > Not true for async data though. Absolutely true for async data! I've seen this exact problem in telecom interfaces I've worked on. Async interfaces are not a good match for continuous data, because of this specific problem. If the application actually requires continuous streams of data >632 bytes, then the approach we took was to implement an async transmitter (in our FPGA) that actually transmitted stop bits that were slightly short, allowing the next byte to start a little early if necessary. This won't be an option with the 3100, of course, so it will be necessary to give it a crystal that's a little on the high side. > You only care how far you are apart at the end of the byte. That's true only for receiving. The problem here is that the MAX3100 is taking slightly longer to retransmit the data compared to how fast the modem is sending it to the PIC. -- Dave Tweed -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist