EIA-449 Cable Bus

EIA/TIA-449 Description

EIA/TIA-449; General Purpose 37-Position Interface for 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- or 9-pin connector.
EIA-449 cabling uses EIA-422 differential pairs to send and receive data, and EIA-423 single-ended lines to send and receive control signals.

V.35/RS449 Cable Length Recommendations; The cable length will determine maximum bus speed, or the maximum transfer rate is determined by the cable length (examples): 2Mbps out to 50 feet, 1Mbps to 100 feet, 512kbps to 200 feet, 256kbps to 400 feet, 128kbps to 800 feet, 56kbps to 1600 feet, 1.2kbps to 3000 feet.

The V.35 specification also specified a 37 pin connector, but many times was implemented with a DB25 with a non-standard pinout. I believe V.35 was replaced by the V.10/V.11 standards. The 34-pin MRAC connector is listed on the V.35 page.

EIA-449 9 Pin Connector Pin Out
Pin Signal Name Signal Function Pin Signal Name Signal Function
1 Shield Ground - - -
2 Sec Receive Ready Control from DCE 6 Receive Common Ground
3 Sec Send Data Data to DCE 7 Sec Request to Send Control from DCE
4 Sec Receive Data Data from DCE 8 Sec Clear to Send Control from DCE
5 Signal Ground Ground 9 Send Common Ground

RS-449, 37-pin connector Pinout and Signal Names

Normally EIA422 and 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 does not follow 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 499) than the system would revert to EIA423 (single-ended) distance and data rate ~ Only because the driver on the 423 side is single ended, while the receiver on the 422 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.

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.

EIA449 Standard Organizations

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

Electronic Industries Alliance {EIA}, has disbanded in 2011
Telecommunications Industry Association {TIA}, www.tiaonline.org

EIA449 Interface ICs

EIA-449 is a cable bus. The specification only define the physical interconnect, the electrical interface is defined in other documents. In this case EIA-422, EIA-423, EIA485, and EIA-232 define the electrical interface [ICs].
For a listing of Interface or driver IC manufacturers refer to one of the following electrical pages [located on this site]:
RS-232 Bus description, the RS-422 / RS485 Cable Bus, or the RS-423 Cable Bus

{Back to EIA-449 Index}

PC motherboard

Distributor rolodex Electronic Components Electronic Equipment EDA CDROM Software Engineering Standards, BOB card Cabled Computer Bus Electronic Engineering Design Table Conversion DB9-to-DB25.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 3/04/12
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