CL4424 User’s Manual

2. Interfacing Protocol

The CL4424 is a DCE (Data Communications Equipment). A DCE can be interfaced to a DTE using a straight through serial cable (the serial cable provided with the CL4424 is a straight through cable). Typically, PC’s are defined as a DTE and peripherals are defined as DCE. To interface a DCE with another DCE, or a DTE with another DTE, a null modem (or a Crossover) cable is required. The null modem simply swaps pins to convert a DCE to a DTE and vice-versa. A null modem cable can be provided with the CL4424 on request.

The CL4424 transceivers support the following interface protocols

RS-232

RS-485 (2-wire) Half Duplex

Table 1 – DTE, DCE and Null Modem Signal Definitions

DCE Pin

DCE Signal

DCE

DTE Pin

DTE Signal

DTE

Null Modem

Null Modem

Number

Name

Direction

Number

Name

Direction

Female DB9

Male DB9

 

 

 

 

 

 

 

 

1

DCD

O

1

DCD

I

1

NC

 

 

 

 

 

 

 

 

2

TXD

O

2

RXD

I

2

3

 

 

 

 

 

 

 

 

3

RXD

I

3

TXD

O

3

2

 

 

 

 

 

 

 

 

4

DTR

I

4

DTR

O

4

6

 

 

 

 

 

 

 

 

5

GND

 

5

GND

 

5

5

 

 

 

 

 

 

 

 

6

DSR

O

6

DSR

I

6

4

 

 

 

 

 

 

 

 

7

RTS

I

7

RTS

O

7

8

 

 

 

 

 

 

 

 

8

CTS

O

8

CTS

I

8

7

 

 

 

 

 

 

 

 

9

RI

O

9

RI

I

9

NC

 

 

 

 

 

 

 

 

6/21/2005

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AeroComm CL4424 user manual Interfacing Protocol, DTE Pin DTE Signal, Null Modem