EIA-423 Bus

Electrical Characteristics of Unbalanced Voltage Digital Interface Circuits

[EIA423 Description] [EIA423 Interface ICs]
[Standard Organizations] [RS449 Cabling]

EIA/TIA-423 Description

The EIA/TIA-423 Unbalanced (Single-Ended) interface; specifies a single, unidirectional driver with multiple receivers (up to 10). "..Specifies the electrical characteristics of the unbalanced voltage digital interface circuit, normally implemented in integrated circuit technology, that may be employed when specified for the interchange of serial binary signals between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) or in any point-to-point interconnection of serial binary signals between digital equipment." 'Telecommunications Industry Association'
EIA-423 is used in EIA-449 and EIA530, both of which define the cabling and pin-out to form a complete interface. As EIA-423 does not define a cable.

EIA-423 Interface Standard implementation Circuit Schematic
EIA/TIA-423 Interface Circuit

EIA/TIA-423 Standard Organizations

ANSI/TIA/EIA-423-B-96 Electrical Characteristics of Unbalanced Voltage Digital Interface Circuits

Telecommunications Industry Association; TIA [www.tiaonline.org]

Note the Electronic Industries Alliance {EIA} ceased operations on Feb 22 2011.
So the proper spec name would be TIA-423, without the reference to EIA.

V.10: Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to 100 kbit/s

ITU {International Telecommunication Union}, www.itu.int

The correct term for this standard is ANSI/TIA/EIA-423, how ever short hand leads to ANSI-423, TIA-423, or EIA-423 [obsolete reference].
In many cases the term RS-423 may also be seen. RS-423 is in common usage, but has been out-dated for more then 20 years.
The term RS means Recommended Standard.

FED STD 1020A is identical to TIA/EIA-423-B. It is intended for United States, non-military government use.
FED STD 1030A is identical to TIA/EIA-422-B. It is intended for United States, non-military government use.

{RS423 Bus Index}

EIA/TIA-423 Bus Interface IC Manufacturers

EIA-423 Interface Voltage Standard
EIA/TIA-423 Switching Levels

I/O Chip Vendors:
Linear Technology {EIA422 Transceiver-Driver-Receiver IC Manufacturer}

Maxim {RS423 ICs, multi-protocol cable termination networks}

National Semiconductor {EIA-422 Differential Bus Transceiver-Receiver-Driver IC Manufacturer}

ON Semiconductor {EIA562-EIA422/EIA423 IC Manufacturer}

Texas Instruments 'TI' {RS-423/RS-422 ICs}

{RS423 Bus Index}

EIA422 / EIA423 Cabling

EIA/TIA-449; General Purpose 37-Position Interface fro Data terminal Equipment and Data Circuit-Terminating Equipment Employing Serial binary Data Interchange

A serial mechanical interface standard for transmission of balanced and unbalanced signals between a variety of higher-end computer, media, and multimedia peripherals.
EIA-449 allows a maximum data rate of 10 Mbit/s and uses a 37-pin or 9-pin connector.
RS-449, 37pin pinout
RS-449, 9pin pinout

EIA/TIA-530; High Speed 25-Position Interface for Data Terminal Equipment and Data Circuit-Terminating Equipment, Including Alternative 26-Position Connector

EIA530 is a replacement for EIA-449 that uses a DB-25 (EIA-232-D) connector instead of a 37-pin connector, while keeping the most important electrical signals intact.
RS-530, 25 pin pinout
EIA-530 is to be used in conjunction with EIA-422-A.

V.35/RS449 Max length
Data Rate Cable Length
2 Mb/sec 15.24 Meters
1 Mb/sec 30.48 Meters
512 Kb/sec 60.96 Meters
256 Kb/sec 121.92 Meters
128 Kb/sec 243.84 Meters
56 K 487.68 Meters
1.2 Kb/sec 914.40 Meters

Design Suggestion; To increase the possible data rate use a balanced transmission scheme like RS422.

{RS423 Bus Index}

Normally EIA422 and RS-423 systems may not be connected together. EIA-449 cabling of 422 sends and receives data as differential pairs and control signal as single-ended, but for 423 cabling it sends and receives single-ended data and control signals. Receiving the single ended signal in 423 is accomplished by grounding the 'B' side of the differential receiver at the connector.

So if the system follows the EIA-449 (cabling) specification than one (B) side of the differential receiver of the 423 side will be grounded at the connector forcing the differential driver on the 422 side to drive ground. The EIA422 side also uses a termination resistor between the ends of its differential receiver, providing a serious 120 ohm short to ground for the 423 driver.

If the systems were to be connected together (with out regard for RS499) than the system would revert to EIA423 (single-ended) distance and data rate ~ Only because the driver on the RS423 side is single ended, while the receiver on the RS422 side would receive the single-ended 423 signal and ground on its differential pair.
How ever because 423 and 422 use the same receiver chip; going from 422 to 423 provides a differential path.

RS423 to RS422 Conversion

{Back to RS423 Interface Bus Index}

Design Note; The polarity of the RS423 signal may be inverted by swapping the two incoming lines on the RS422 receiver.

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Modified 6/13/15
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