20mA current loop serial line interface - Revision history

Jonathanjo: fixed typo

2024-09-26T14:57:21Z

fixed typo

Jnc: New cat

2022-05-23T13:01:23Z

New cat

Jnc: add active/passive

2021-08-11T21:15:47Z

add active/passive

Jnc: better car

2018-12-13T19:00:54Z

better car

Jnc: +cat

2018-12-13T15:14:25Z

+cat

Jnc: Avoid redir

2018-04-25T13:08:31Z

Avoid redir

Jnc: A decent start

2017-01-15T16:03:25Z

A decent start

New page

The '''20mA current loop serial line interface''' was an early standard (de facto, not formal) electrical system for [[asynchronous serial line]]s between terminals and computers. It was made popular by the [[Model 33 Teletype]].

Current loop interface, as the name implies, used the presence or absence of a current to encode signals, rather than voltage (as used in the [[EIA RS-232 serial line interface]]). The first current loop interfaces used a 60mA current, but this was later reduced to 20mA.

The absence of a current signals space (or high), and the presence of a current is used for mark (low). Thus, in the idle (mark) state (the normal for most lines, most of the time), no power is consumed.

Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.

@@ Line 11: / Line 11: @@
 A current loop channel has 3 main components; a current source, a switch, and a detector. The component which is the source of the data (the keyboard, in a terminal; the computer, for an output channel, e.g. to the printer of a terminal) will include the switch; the consumer of the data (the printer, in the output channel case) will include the detector.
-''Either end of the channel can have the current source''; the term 'active' is usually used to indicate that end. So an 'active receiver' would be one that includes a current source, and similarly an 'active transmitter'. Both receivers and transmitters can also be 'passive'. Normally, in a bi-directional link, both channels will have their active and passive ends at the same end of the limk, and so the entire interface is described as 'active' or 'passive'.
+''Either end of the channel can have the current source''; the term 'active' is usually used to indicate that end. So an 'active receiver' would be one that includes a current source, and similarly an 'active transmitter'. Both receivers and transmitters can also be 'passive'. Normally, in a bi-directional link, both channels will have their active and passive ends at the same end of the link, and so the entire interface is described as 'active' or 'passive'.
 [[Category: Serial Lines]]

← Older revision		Revision as of 13:01, 23 May 2022
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	''Either end of the channel can have the current source''; the term 'active' is usually used to indicate that end. So an 'active receiver' would be one that includes a current source, and similarly an 'active transmitter'. Both receivers and transmitters can also be 'passive'. Normally, in a bi-directional link, both channels will have their active and passive ends at the same end of the limk, and so the entire interface is described as 'active' or 'passive'.		''Either end of the channel can have the current source''; the term 'active' is usually used to indicate that end. So an 'active receiver' would be one that includes a current source, and similarly an 'active transmitter'. Both receivers and transmitters can also be 'passive'. Normally, in a bi-directional link, both channels will have their active and passive ends at the same end of the limk, and so the entire interface is described as 'active' or 'passive'.

−	[[Category: ~~Communication Basics~~]]	+	[[Category: Serial Lines]]

@@ Line 1: / Line 1: @@
-The '''20mA current loop serial line interface''' was an early standard (de facto, not formal) electrical system for [[asynchronous serial line]]s between terminals and computers. It was made popular by the [[Teletype|Model 33 Teletype]].
+The '''20mA current loop serial line interface''' was an early standard (de facto, not formal) electrical system for [[asynchronous serial line]]s between [[terminal]]s and computers. It was made popular by the [[Teletype|Model 33 Teletype]].
-Current loop interface, as the name implies, used the presence or absence of a current to encode signals, rather than voltage (as used in the [[EIA RS-232 serial line interface]]). The first current loop interfaces used a 60mA current, but this was later reduced to 20mA.
+Current loop interface, as the name implies, used the presence or absence of a [[current]] to encode signals, rather than [[voltage]] (as used in the [[EIA RS-232 serial line interface]]). The first current loop interfaces used a 60mA current, but this was later reduced to 20mA.
 The absence of a current signals space (or high), and the presence of a current is used for mark (low). Thus, in the idle (mark) state (the normal for most lines, most of the time), no power is consumed.
 Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.
 [[Category: Communication Basics]]

← Older revision		Revision as of 19:00, 13 December 2018
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	Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.		Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.

−	[[Category: ~~Device Basics‎‎~~]]	+	[[Category: Communication Basics]]

← Older revision		Revision as of 15:14, 13 December 2018
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	Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.		Its main advantages are that it can be used over long distances, and in such applications, line losses are not problematic. Its main disadvantage is that high speeds cannot be used over long distances, as they can with voltage-based systems like RS-232.
		+
		+	[[Category: Device Basics‎‎]]

← Older revision		Revision as of 13:08, 25 April 2018
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−	The '''20mA current loop serial line interface''' was an early standard (de facto, not formal) electrical system for [[asynchronous serial line]]s between terminals and computers. It was made popular by the [[Model 33 Teletype]].	+	The '''20mA current loop serial line interface''' was an early standard (de facto, not formal) electrical system for [[asynchronous serial line]]s between terminals and computers. It was made popular by the [[Teletype\|Model 33 Teletype]].

	Current loop interface, as the name implies, used the presence or absence of a current to encode signals, rather than voltage (as used in the [[EIA RS-232 serial line interface]]). The first current loop interfaces used a 60mA current, but this was later reduced to 20mA.		Current loop interface, as the name implies, used the presence or absence of a current to encode signals, rather than voltage (as used in the [[EIA RS-232 serial line interface]]). The first current loop interfaces used a 60mA current, but this was later reduced to 20mA.