Siemens Simatic S7-200 System Manual page 50

Installing and Using the STEP 7-Micro/WIN Software
Depending on whether you want to connect to only one S7-200 CPU or to a network of them,
you need the following cables and adapter (see Figure 3-14):
A cable with RS-232 capability at each end to connect the PC or SIMATIC programming
device to a full-duplex 11-bit modem at one end of the telephone line
A null modem adapter to connect the modem at the other end of the telephone line to a
PC/PPI cable
A PC/PPI cable to connect the null modem adapter to either of the following ports:
– The communications port of the S7-200 CPU (see Figure 3-14)
– A Siemens programming port connector on a PROFIBUS network (see Figure 9-3)
RS-232
COMx
PG/
PC
Note: x = your port number
Figure 3-14
Because these configurations allow only one master device, there is no token passing.
These configurations support only the PPI protocol. In order to communicate through the PPI
interface, the S7-200 programmable logic controller requires that the modem use an 11-bit
data string. The S7-200 controller requires one start bit, eight data bits, one parity bit (even
parity), one stop bit, asynchronous communication, and a transmission speed of 9600 baud
for PPI. Many modems are not capable of supporting this data format. The modem requires
the settings listed in Table 3-3.
Figure 3-15 shows the pin assignments for a null modem adapter. For more information on
network communications using the PC/PPI cable, see Chapter 9.
Table 3-3
Data Format in Bits
8 data
1 start
1 stop
1 parity (even)
3-20
Telephone line
Full-duplex
11-bit
modem
RS-232
Local
S7-200 Data Communications Using an 11-Bit Modem
Modem Settings Required
Transmission Speed
between Modem and PC
9600 baud 9600 baud
Null modem PC/PPI
adapter cable
Full-duplex
11-bit
modem
RS-232
Remote
Transmission Speed on
the Line
9600 baud 9600 baud
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
CPU 214
Other Features
Ignore DTR signal
No hardware flow
control control