Specifications

APPENDIX B: Electrical Interfaces

B.2 RS-422

The RS-422 specification defines the electrical

characteristics of balanced voltage digital interface

circuits. RS-422 is a differential interface that defines

voltage levels and driver/receiver electrical

specifications. On a differential interface, logic levels are

defined by the difference in voltage between a pair of

outputs or inputs. In contrast, a single-ended interface

(such as RS-232) defines the logic levels as the

difference in voltage between a single signal and a

common ground connection. Differential interfaces are

typically more immune to noise or voltage spikes that

may occur on the communication lines. Differential

interfaces also have greater drive capabilities that allow

for longer cable lengths. RS-422 is rated up to 10 Mbps

and can have cabling 4000 feet (1219.2 m) long. RS-422

also defines driver and receiver electrical characteristics

that will allow one driver and up to 32 receivers on the

line at once. RS-422 signal levels range from 0 to +5

volts. RS-422 does not define a physical connector.