Siemens SIMATIC S7 System Manual page 200

Program instructions
7.3 Communication
Non-fatal errors with ENO = 0
0006H Indirect address
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0009H Simultaneous Trans-
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mit/Receive on port 0
000BH Simultaneous Trans-
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mit/Receive on port 1
0090H Port number is invalid
•
Receive parameter error sets
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SM86.6 or SM186.6
CPU is not in Freeport mode
•
Input / output
TBL
PORT
Using Freeport mode to control the serial communications port
You can select the Freeport mode to control the serial communications port of the CPU by
means of your user program. When you select Freeport mode, your program controls the
operation of the communications port through the use of the receive interrupts, the transmit
interrupts, the Transmit instruction, and the Receive instruction and entirely controls the
communications protocol while in Freeport mode. You use SMB30 and SMB130 to select the
baud rate and parity.
The CPU assigns two special memory bytes to the two physical ports:
● SMB30 to the integrated RS485 port (Port 0)
● SMB130 to the CM01 RS232/RS485 Signal Board (SB) port (Port 1)
The Freeport mode is disabled and normal communications are re-established (for example,
HMI device access) when the CPU is in STOP mode.
In the simplest case, you can send a message to a printer or a display using only the
Transmit (XMT) instruction. Other examples include a connection to a bar code reader, a
weigh scale, and a welder. In each case, you must write your program to support the
protocol that is used by the device with which the CPU communicates while in Freeport
mode.
200
SM bits affected
SM 86.6 Receive message terminated on port 0
•
SM 186.6 Receive message terminated on port 1
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Data type Operand
BYTE IB, QB, VB, MB, SMB, SB, *VD, *LD, *AC
BYTE Constant: 0 or 1
Note: The two available ports are as follows:
Integrated RS485 port (Port 0),
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CM01 Signal Board (SB) RS232/RS485 port (Port 1)
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART