4 ms·
Actually, there was an even older style of tty interface derived from telegraph circuits and called "current loop" that the ASR-33 originally used; in the 1970s
by jgrahamc 3y ago
Actually, there was an even older style of tty interface derived from telegraph circuits and called "current loop" that the ASR-33 originally used; in the 1970s dual-mode ASR-33s that could also speak RS-232 began to ship, and RS-232 eventually replaced current loop entirely.
This is what the KIM-1 (https://en.wikipedia.org/wiki/KIM-1 https://en.wikipedia.org/wiki/KIM-1) uses and it's pretty common for current loop (https://en.wikipedia.org/wiki/Current_loop https://en.wikipedia.org/wiki/Current_loop) interfaces to still be used in the context of industrial control and it's also the basis for MIDI (https://en.wikipedia.org/wiki/MIDI#Electrical_specifications https://en.wikipedia.org/wiki/MIDI#Electrical_specifications).
- ajb 3y agoCurrent loop is used where the length of the cable could be huge. If you put in 20mA at one end, you know you will get it out at the other irrespective of length, which is not true of voltage.
- dboreham 3y agoCurrent loop was commonly used into the 80s : anywhere that needed a long cable run. From memory a VAX 780 could do 19200 but only over 20mA loop.