Siemens SIMATIC S7-200 System Manual page 246

S7-200 Programmable Controller System Manual
Switch 6 of the RS-232/PPI Multi-Master cable
allows you to set the RS-232 port of the cable to
either Local (DCE) or Remote (DTE) mode.
If you are using the RS-232/PPI Multi-Master
-
cable with STEP 7--Micro/WIN or if the
RS-232/PPI Multi-Master cable is connected
to a computer, set the RS-232/PPI
Multi-Master cable to Local (DCE) mode.
If you are using the RS-232/PPI Multi-Master
-
cable with a modem (which is a DCE device),
set the RS-232/PPI Multi-Master cable to
Remote (DTE) mode.
This eliminates the need to install a null modem adapter between the RS-232/PPI Multi-Master
cable and the modem. Depending on the connector on the modem, you might still need to use a
9-pin-to-25-pin adapter.
Figure 7-30 shows the pin assignment for a common modem adapter.
See Appendix A for more information about the RS-232/PPI Multi-Master cable. The pin numbers
and functions for the RS-485 and RS-232 ports of the RS-232/PPI Multi-Master cable in Local
(DCE) mode are shown in Table A-69. Table A-70 shows the pin numbers and functions for the
RS-485 and RS-232 ports of the RS-232/PPI Multi-Master cable in Remote (DTE) mode. The
RS-232/PPI Multi-Master cable supplies RTS only when it is in Remote (DTE) mode.
Using a Radio Modem with the RS-232/PPI Multi-Master Cable
You can use an RS-232/PPI Multi-Master cable to connect the RS-232 communications port of a
radio modem to an S7-200 CPU. However, operation with radio modems is not the same as it is
with telephone modems.
PPI Mode
With the RS-232/PPI Multi-Master cable set for PPI mode (switch 5 = 1), you would normally
select remote mode (switch 6 = 1) for operation with a modem. However, selecting the remote
mode causes the cable to send the character string 'AT' and wait for the modem to reply with 'OK'
on each power up. While telephone modems use this sequence to establish the baud rate, radio
modems do not generally accept AT commands.
Therefore, for operation with radio modems you must select local mode (switch 6 = 0) and use a
null modem adapter between the RS-232 connector of the cable and the RS-232 port on your
radio modem. Null modem adapters are available in either 9-pin-to-9 pin or 9-pin-to-25 pin
configurations.
Configure the radio modem to operate at 9.6, 19.2, 38.4, 57.6 or 115.2 kbaud. The RS-232/PPI
Multi-Master cable will automatically adjust to any one of these baud rates on the first character
transmitted by the radio modem.
PPI/Freeport Mode
With the RS-232/PPI Multi-Master cable set for PPI/Freeport mode (switch 5 = 0), select remote
mode (switch 6 = 1) for operation with a radio modem. Configure the cable so that it will not send
any AT commands to setup the modem.
Switches 1, 2, and 3 on the RS-232/PPI Multi-Master cable set the baud rate. See Figure 7--29.
Select the baud rate setting that corresponds to the baud rate of the PLC and the radio modem.
232
RS-485
S7-200
9-pin-to-25-pin adapter
9-pin
25-pin
RD 2
2 TD
TD 3
3 RD
RTS 7
4 RTS
GND 5
7 GND
Figure 7-30 Pin Assignments for Adapters
RS-232
DCE
Modem
(input to DCE)
(output from DCE)