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:
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: