3 ms·

https://www.optcore.net/difference-between-rs-232-rs-422-and-rs-485/#:~:text=What%20is%20the%20difference%20between,the%20single%2Dended%20transmission%20mode h

by dgfitz 2y ago

https://www.optcore.net/difference-between-rs-232-rs-422-and-rs-485/#:~:text=What%20is%20the%20difference%20between,the%20single%2Dended%20transmission%20mode https://www.optcore.net/difference-between-rs-232-rs-422-and.... Serial is usually ascii, not always but usually. The different types of serial depend on things like duplexity and line noise, or lack thereof. 232 is -15v to 15v, 422 is -6 to 6, and 485 is -7 to 12

YZF 2y ago
RS422 and RS485 use the same differential signalling IIRC. The difference between two lines (>some mV <some mV) is what encodes zero or one. There's some allowed voltage range defined from ground but it's not that level that encodes the signal, it's the difference. Running a differential signal over a twisted pair reduces the noise. In RS232, to contrast, the voltage defines the values, +/- 12V is also common and I think you can go pretty low while still meeting the standard. ASCII is orthogonal, you can send anything over the serial link. EDIT: apparently 3V-15V are the defined voltage levels (-3V - -15V) and drivers should tolerate up to +/-25V.
- Gibbon1 2y ago
  Big difference between RS422 and RS485 is the drivers for RS485 are required to survive a minus 7 volt difference between the two grounds. Old R422 drivers would smoke if you got more than 7 tenths of a volt difference. Which would happen if you had a open ground. Or lighting hit. Or some big motor turned on. We had an RS422 based system with 50 units on one pair. One of them was holding the line. Coworker unplugged each one till he found it. And half of them didn't work after that.
epcoa 2y ago
For years the most common use for “serial” would be dialup internet and computer mice (among other peripherals), neither of which would have been primarily ASCII. Not sure what you have in mind by “usually” ASCII, but it’s not the layer that serial links operate at, they’re just a dumb pipe.

by dgfitz 2y ago

YZF 2y ago

RS422 and RS485 use the same differential signalling IIRC. The difference between two lines (>some mV <some mV) is what encodes zero or one. There's some allowed voltage range defined from ground but it's not that level that encodes the signal, it's the difference. Running a differential signal over a twisted pair reduces the noise. In RS232, to contrast, the voltage defines the values, +/- 12V is also common and I think you can go pretty low while still meeting the standard. ASCII is orthogonal, you can send anything over the serial link. EDIT: apparently 3V-15V are the defined voltage levels (-3V - -15V) and drivers should tolerate up to +/-25V.

Gibbon1 2y ago
Big difference between RS422 and RS485 is the drivers for RS485 are required to survive a minus 7 volt difference between the two grounds. Old R422 drivers would smoke if you got more than 7 tenths of a volt difference. Which would happen if you had a open ground. Or lighting hit. Or some big motor turned on. We had an RS422 based system with 50 units on one pair. One of them was holding the line. Coworker unplugged each one till he found it. And half of them didn't work after that.

epcoa 2y ago

For years the most common use for “serial” would be dialup internet and computer mice (among other peripherals), neither of which would have been primarily ASCII. Not sure what you have in mind by “usually” ASCII, but it’s not the layer that serial links operate at, they’re just a dumb pipe.