6502.org

Garth,

My experience with B&B Electronics has been excellent. I've used several of their RS-485 products including their single-port RS-485 PCI card and both versions of the RS-232 to RS-485 converter. I have a DB9 inline RS-232 tester from them that I use all the time. Their website is also a good source for documentation on RS-485 and their staff is good to work with.

B&B also resells an Ethernet to serial hub under the RocketPort label that is made by Comtrol and comes in 4- or 8-port versions. The "Si" model is software-selectable for RS-232 or RS-485. I have three of these hubs (24 serial ports) coexisting on a Windows 2000 machine and they have not given me trouble.

One product I stay away from now is their USB to RS-485 converter. It's fine for home or light duty use but I had it in an automated test system that used it continuously and it would intermittently lock up the computer due to driver issues.

Regards,
Mike

>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.