Siemens SIMATIC S7 System Manual page 201

You can only use Freeport communications when the CPU is in RUN mode. Enable the
Freeport mode by setting a value of 01 in the protocol select field of SMB30 (Port 0) or
SMB130 (Port 1). While in Freeport mode, you cannot communicate with an HMI on the
same port.
Note
The serial CR model CPUs disable Freeport mode when you connect a USB-PPI cable to
the CPU. Likewise, the CPU inhibits the switch to Freeport mode if you connect a USB-PPI
cable to the CRs CPUs.
Changing PPI communications to Freeport mode
SMB30 and SMB130 configure the communications ports, 0 and 1 respectively, for Freeport
operation and provide selection of baud rate, parity, and number of data bits. The following
figure describes the Freeport control byte. One stop bit is generated for all configurations.
pp
bbb
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
Parity select
00 = No parity
01 = Even parity
10 = No parity
11 = Odd parity
Freeport baud rate
000 = 38400
001 = 19200
010 = 9600
011 = 4800
100 = 2400
101 = 1200
110 = 115200
111 = 57600
d Data bits per character
0 = 8 bits per character
1 = 7 bits per character
mm Protocol selection
00 = PPI slave mode
01 = Freeport mode
10 = Reserved (defaults to PPI slave mode)
11 = Reserved (defaults to PPI slave mode)
Program instructions
7.3 Communication
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