tnixon@hayes.uucp (01/30/91)
In article <6677.27A3B01E@zswamp.fidonet.org>, root@zswamp.fidonet.org (Geoffrey Welsh) writes: > >The best choice will probably be EIA-530. This uses the > >same 25- or 26-pin connector as EIA-232, but uses EIA-422 (balanced) > >circuits for signals that change quickly (data, clocks) and EIA-423 > >(unbalanced) circuits for signals that don't change as often > >(DTR, DCD, etc.) > > Do we really need a mongrel serial design? Is the cost of going whole-hog > balanced that high that we can't afford the consistency? Well, of course, RS-449 was "whole-hog" -- every signal balanced. But almost nobody but the government and some phone switch manufacturers ever used it, because nobody wanted to make space on their devices for the huge 39-pin connector -- which is inescapable if you make all signals balance. There really is no _need_ to balance signals that only change once per connection, like DSR, DTR, DCD, RI, etc., so why pay the cost both in connector space and in wires? Cabling is expensive! > >There are similar buffered devices from > >other companies, but most of them don't preserve backward > >compatibility with existing comm software (which ESP does). > > Then I don't suppose that the ESP uses the 16550's DMA mode? To be perfectly honest, I'm not aware that 16550s _have_ any built-in DMA mode. They have 16-byte FIFOs, and the ability to transfer multiple bytes during a single interrupt cycle, but my understanding was that this was handled through byte-at-a-time accesses from the CPU, not by DMA. -- Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net