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Chapter 7 EIA-422 Asynchronous Interface 29

General EIA-422 Cable Information

This section applies to Digi products equipped with EIA-422 asynchronous

interfaces.

Physical Cable Characteristics

EIA-422 interface cables should be shielded twisted-pair cables. Each

signal requires two leads (one twisted pair of wires) to complete a balanced

voltage digital circuit. The shield should be connected to the Chassis

Ground of the devices at both ends of the interface cable.

Interface Signaling

The EIA-422 interface provides four signals: Transmitted Data (TxD),

Received Data (RxD), Request To Send (RTS) and Clear To Send (CTS).

The functions of these signals are identical to their EIA-232 counterparts.

Grounding Requirements

EIA-422 interface cables must provide a ground path between the devices

to be connected. This ensures the integrity of data transfers and control

signals. This should be connected to the Chassis Ground of each device.

Digi recommends using the cable shield for this purpose.

Digi EIA-422 Connector Wiring

A terminal, a serial printer, or a serial port for another computer usually

functions as a DTE device. The Digi adapter is also a DTE device. To

connect a DTE device to another DTE device a null modem cable or

adapter must be used.

Two wires (one twisted pair) are required for each signal, a positive lead

("+"), and a negative lead ("-"). The "+" leads at one end of the cable must

be connected to the "+" leads at the other end, and the "-" leads at one end

must be connected to the "-" leads at the other end.

Incorrect wiring could result in damage to the connected devices. The

following table shows the pin configurations for the EIA-422 versions of

Digi DB-9, DB-25, and RJ-45 connectors.

Chapter 5

EIA-422 Asynchronous Interface

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RTS XCP-48-RJ45 Spécifications Page 29