Setting Up Communications Hardware and Network Communications
7-41
S7-200 Programmable Controller System Manual
A5E00066097-02
Using a Modem with a 4-Switch PC/PPI Cable
You can use a 4-switch PC/PPI cable to connect the RS-232 communication port
of a modem to an S7-200 CPU. Modems normally use the RS-232 control signals
(such as RTS, CTS, and DTR) to allow a PC to control the modem. This PC/PPI
cable does not use any of these signals, so when you use a modem with a
4-switch PC/PPI cable, the modem must be configured to operate without these
signals. As a minimum, you must configure the modem to ignore RTS and DTR.
Consult the operator manual supplied with the modem to determine the commands
required to configure the modem.
A modem is classified as Data Communications Equipment (DCE). The RS-232
port of the 4-switch PC/PPI cable is also classified as DCE. When you connect two
devices of the same class (both DCE), the transmit data and receive data pins
must be swapped. A null modem adapter swaps these lines. See Figure 7-28 for a
typical setup and the pin assignment for a null modem adapter.
Modem
RS-232
PC/PPI
cable
9 pin
2
3
5
25 pin
2 TD
3 RD
4 RTS
5 CTS
6 DSR
8 DCD
20 DTR
7 GND
Null modem
9-pin to 25-pin adapter
S7-200
Figure 7-28 11-Bit Modem with a Combination Null Modem and a 9-pin to 25-pin Adapter
To Next Page
Loading...
