>John, do you have any experience with B&B Electronics' serial
>interfacing products? (like RS-232 to RS-485?) They've been
>sending me catalogs for years. The products look quite interesting
>but I've never jumped in.
I'd never even heard of them :-) We rolled our own everything, using the 75176 transceiver (8 pin, TTL levels on one side, RS485 on the other). Our 232 to 485 converter used the RTS line to control direction. Since we wrote all the software, we had control over everything and didn't need anything fancier.
The converter was basically a MAX232 and a 75176 stuck together, with a power supply and a bit of lightning protection. Those km of cables were typically buried just under the ground, on golf-courses, which are known to be lightning magnets.
If you wanted to use 485 without a UART, I'd recommend stringing two cables (or use four wires from one), with data on one pair and a clock on the other. Or you could use one pair and a self-clocking scheme like GCR (the 1541 disk drive used it). Map 8 bits of input to 10 or so bits of output, with the property that you never have more than some small number of 0s or 1s in a row. Use a timer to tell you when each bit should start, and reset it on every edge that you see in the input. The limited runs of 0s and 1s mean the clock won't get a chance to drift far before it's resynchronised.
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