EIA-422
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EIA-422 (formerly RS-422) is a serial data communication protocol which specifies 4 wire, full-duplex, differential line, multi-drop communications. It provides for balanced data transmission with unidirectional/non-reversible, terminated or non-terminated transmission lines. In contrast to RS485 (which is multi-point instead of multi-drop) EIA-422 does not allow multiple drivers but only multiple receivers.
| Application layer | HTTP, HTTPS, SMTP, FTP, UUCP, NNTP, SSH, IRC, SNMP, SIP, RTP, Telnet ,... |
| Transport layer | TCP, UDP, SCTP, DCCP, ... |
| Network layer | IPv4, IPv6, ICMP, ARP, IGMP, ... |
| Data link layer | Ethernet, Wi-Fi, Token ring, FDDI, PPP, ... |
| Physical layer | RS-232, EIA-422, RS-449, EIA-485... |
Several key advantages offered by this standard include the differential receiver defined in RS-423, a differential driver and data rates as high as 10 Megabaud at 12 metres (40 ft).
The mechanical connections for this interface are specified by EIA-530 (DB-25 connector) or EIA-449 (DB-37 connector), however devices exist which have 4 screw-posts to implement the transmit and receive pair only. The maximum cable length is 1200 m. Maximum data rates are 10 Mbit/s at 1.2 m or 100 kbit/s at 1200 m. EIA-422 cannot implement a truly multi-point communications network (such as with EIA-485), although only one driver can be connected to up to ten receivers.
A common use of EIA-422 is for RS-232 extenders. Also, an RS-232-compatible variant of RS-422 using a mini-DIN-8 connector was widely used on Macintosh hardware until it was replaced by Intel's Universal Serial Bus on the iMac.
- This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.