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 CL44 24 i s 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