Siemens S7-1200 System Manual page 673

The STEP 7 user program can also configure the port or change the existing configuration
with the PORT_CFG instruction (Page 686).
Note
Parameter values set from the PORT_CFG instruction in the user program override port
configuration settings set from the device configuration. Note that the S7-1200 does not
retain parameters set from the PORT_CFG instruction in the event of power down.
Parameter
Baud rate
Parity
Data bits per character
Number of stop bits
Flow control
Wait time
Operating mode
Receive line initial state
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Definition
The default value for the baud rate is 9.6 Kbits per second. Valid choices are: 300 baud,
600 baud, 1.2 Kbits, 2.4 Kbits, 4.8 Kbits, 9.6 Kbits, 19.2 Kbits, 38.4 Kbits, 57.6 Kbits, 76.8
Kbits, and 115.2 Kbits.
The default value for parity is no parity. Valid choices are: No parity, even, odd, mark (parity
bit always set to 1), and space (parity bit always set to 0).
The number of data bits in a character. Valid choices are 7 or 8.
The number of stop bits can be either one or two. The default is one.
For the RS232 communication module, you can select either hardware or software flow
control (Page 674). If you select hardware flow control, you can select whether the RTS
signal is always on, or RTS is switched. If you select software flow control, you can define
the XON and XOFF characters.
The RS485 communication interfaces do not support flow control. The 422 mode of the CM
1241 RS422/485 module supports software flow control.
Wait time specifies the time that the CM or CB waits to receive CTS after asserting RTS, or
for receiving an XON after receiving an XOFF, depending on the type of flow control. If the
wait time expires before the communication interface receives an expected CTS or XON,
the CM or CB aborts the transmit operation and returns an error to the user program. You
specify the wait time in milliseconds. The range is 0 to 65535 milliseconds.
This selects the operating mode RS422 or RS485 and network configurations.
This selects the bias options. Valid values are none, forward bias and reverse bias.
Reverse bias is used to allow cable break detection.
Communication processor and Modbus TCP
12.3 Point-to-point (PtP) communication
Select "Port configuration" to edit the following
RS422/485 parameters:
• "Operating mode":
– Full duplex (RS422) four wire mode (point-to-
point connection)
– Full duplex (RS422) four wire mode (multipoint
master)
– Full duplex (RS422) four wire mode (multipoint
slave)
– Half duplex (RS485) two wire mode
• "Receive line initial state":
– None
– Forward bias (Signal R(A) 0V, signal R(B) 5V)
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