Every time I design a product with an RS485 interface, I wind up going over the same old ground in disbelief - and coming up with the same answer. The A/B line-naming convention is reversed when comparing extant devices (e.g. the venerable SN75176B, or the transceiver product line from Maxim) with the RS485 (ok, EIA485) specification.
Perhaps this confusion stems from the definitions and interpretation of MARK and SPACE. But even avoiding those entirely, I'm still left with the fact that the idle state of an RS485 line involves A being low and B being high. When using e.g. a Maxim part with failsafe inputs (which force the idle state when disconnected) I always have to cross the A/B lines to bring them out of the product. (With the 75176 I can either do that, or invert the Tx/Rd UART signals. The former is easier ;).)
Yet a doubt remains - surely there should be more noise about this issue than I've seen. Anybody feel that this a serious trap for the newbie who doesn't have the actual RS485 spec to hand?
Steve