CL4424 User’s Manual
6/21/2005
10
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
Number
DCE Signal
Name
DCE
Direction
DTE Pin
Number
DTE Signal
Name
DTE
Direction
Null Modem
Female DB9
Null Modem
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
