[cctalk] Re: RS232 then and now

On 2/1/25 02:31, Frank Leonhardt via cctalk wrote: The veneered and generated Intel 8251 is a USART--as were other similar chips (8274, Zilog SIO, etc.)--capable of both asynchronous and asynchronous data transfer. Synchronous for block/bulk transfer is far superior in terms of carrying capacity (no start/stop "bits"; note the quotes; asynchronous "stop" is simply a pause between characters) and was very common in the 1960s and 1970s. Many a hobbyist has scrounged a "good deal" used terminal only to find that it was block-mode synchronous. As far as integration, the original LSI chipsets employed separate devices for transmitting and receiving data. Current-loop is probably still employed extensively in heavy industry--better noise immunity and distance. One used to (in the 1970s) be able to purchase off-the-shelf "long haul" modems that converted between EIA signal levels and current-loop. One of the benefits of CL is that detecting a break in the line is simple--not so for the voltage-oriented EIA signalling (RS-442, 232, 449, etc.). The disadvantage is that signalling is done over a single wire pair--no "handshaking signals. If the 25-way DSUB connector bothers you, have a look at RS-449, which employs a 37-way (DC37) connector: https://en.wikipedia.org/wiki/RS-449 --Chuck