Introduction
This page provides information in regards to the RS422 and RS485 standards.
RS422 & RS485 Logic Levels
Logic 1 = (Non-inverting - Inverting) > 200mV
Logic 0 = (Non-inverting - Inverting) < 200mV
Image taken from http://en.wikipedia.org/wiki/RS-485
RS422 & RS485 Idle State
The idle state of RS422 & RS485 is logic 1.
Example of External Pull Up Resistors to Achieve Idle State
Image taken from http://www.maxim-ic.com/app-notes/index.mvp/id/1833
RS422 & RS485 Serial Port Pinouts
There are no standards for connector pinouts for RS422 or RS485.
RS422 & RS485 Signal Specifications
RS-485 and RS-422 Standards |
|
|
Standard |
RS-422 |
RS-485 |
Mode of operation |
Differential Unidirectional, Multipoint |
Differential Full Duplex, Multipoint |
Allowed no. of Tx and Rx |
1 Tx, 10 Rx |
32 Tx, 32 Rx |
Maximum cable length |
4000ft length |
4000ft length |
Maximum data rate |
10Mbps |
10Mbps |
Minimum driver output range |
±2V |
±1.5V |
Maximum driver output range |
±5V |
±5V |
Maximum driver short-circuit current |
150mA |
250mA |
Tx load impedance |
100Ω |
54Ω |
Rx input sensitivity |
±200mV |
±200mV |
Maximum Rx input resistance |
4kΩ |
12kΩ |
Rx input voltage range |
±7V |
-7V to +12V |
Rx logic high |
>200mV |
>200mV |
Rx logic low |
<200mV |
<200mV |
Table taken from http://www.maxim-ic.com/app-notes/index.mvp/id/736
References:
max485.pdf
http://en.wikipedia.org/wiki/RS-422
http://en.wikipedia.org/wiki/RS-485
http://www.maxim-ic.com/app-notes/index.mvp/id/736
http://www.maxim-ic.com/app-notes/index.mvp/id/1833
Views:
RS-485 and RS-422 Standards |
|
|
RS-422 |
RS-485 |
Mode of operation |
Differential Unidirectional |
Differential Full Duplex |
Multipoint |
Multipoint |
Allowed no. of Tx and Rx |
1 Tx, 10 Rx |
32 Tx, 32 Rx |
Maximum cable length |
4000ft length |
4000ft length |
Maximum data rate |
10Mbps |
10Mbps |
Minimum driver output range |
±2V |
±1.5V |
Maximum driver output range |
±5V |
±5V |
Maximum driver short-circuit current |
150mA |
250mA |
Tx load impedance |
100Ω |
54Ω |
Rx input sensitivity |
±200mV |
±200mV |
Maximum Rx input resistance |
4kΩ |
12kΩ |
Rx input voltage range |
±7V |
-7V to +12V |
Rx logic high |
>200mV |
>200mV |
Rx logic low |
<200mV |
<200mV |
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