Specifications

Setting Up Communications Hardware and Network Communications
7-37
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Using a Modem with a 5-Switch PC/PPI Cable
You can use the 5-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. The PC/PPI
cable does not monitor any of these signals, but does provide RTS in DTE mode.
When you use a modem with a PC/PPI cable, the modem must be configured to
operate without these signals. As a minimum, you must configure the modem to
ignore DTR. Consult the operator manual supplied with the modem to determine
the commands required to configure the modem.
The RS-232 port of the 5-switch PC/PPI cable can be set to either the Data
Communications Equipment (DCE) or Data Terminal Equipment (DTE) mode. The
only signals present on this port are transmit data, Request to Send, receive data,
and ground. The 5-switch PC/PPI cable does not use or supply Clear to
Send (CTS). See Table 7-9 and Table 7-10 for the PC/PPI cable pin-outs.
A modem is classified as Data Communications Equipment (DCE). When you
connect a PC/PPI cable to a modem, the RS-232 port of the PC/PPI cable should
be set to Data Terminal Equipment (DTE), as selected by the DIP switch 5 on the
cable. This eliminates the need for a null modem adapter between the PC/PPI
cable and the modem. You may still require a 9-pin to 25-pin adapter (depending
on the connector on your modem). See Figure 7-25 for a typical setup and the pin
assignment for a 25-pin to 9-pin adapter.
Modem
RS-232
S7-200
PC/PPI
cable
9 pin
2
3
7
5
25 pin
2 TD
3 RD
4 RTS
7 GND
25-pin to 9-pin
Adapter
Figure 7-25 Pin Assignment for a 5-Switch PC/PPI cable With a Modem