Digital current loop interface

Current loops can be used over moderately long distances (tens of kilometres), and can be interfaced with optically isolated links.

There are a variety of such systems, but one based on a 20 mA current level was used by the Teletype Model 33 and was particularly common on minicomputers and early microcomputer which used these as computer terminals.

], current loops were used to send digital data in serial form for teleprinters.

The original IBM PC serial port card had provisions for a 20 mA current loop.

There is no common standard for current loop interfaces, so details such as timing, connectors, wire color codes, and so on, are all application specific.