Siemens S7-1200 System Manual page 737
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- Operating instructions manual (132 pages) ,
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- Manual (46 pages)
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Parameter and type
IP_PORT
IN
MB_HOLD_REG
IN_OUT
NDR
OUT
DR
OUT
ERROR
OUT
STATUS
OUT
MB_SERVER allows incoming Modbus function codes (1, 2, 4, 5, and 15) to read or write
bits and words directly in the input process image and output process image of the S7-1200
CPU. For data transfer function codes (3, 6, and 16), the MB_HOLD_REG parameter must
be defined as a data type larger than a byte. The following table shows the mapping of
Modbus addresses to the process image in the CPU.
Table 12- 57 Mapping of Modbus addresses to the process image
Codes
Function
01
Read bits
02
Read bits
04
Read words Input
05
Write bit
15
Write bits
Incoming Modbus message function codes function codes (3, 6, and 16) read or write words
in a Modbus holding register which can be an M memory address range or a data block. The
type of holding register is specified by the MB_HOLD_REG parameter.
Note
MB_HOLD_REG parameter assignment
The Modbus Holding Register can be in a standard global DB or an M memory address.
For A Modbus holding register in M memory, use the standard Any Pointer format. This is in
the format P#"Bit Address" "Data Type" "Length". An example would be P#M1000.0 WORD
500
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Data type Description
UInt
Default value = 502: The IP port number that identifies the IP port that will be
monitored for a connection request from a Modbus client.
These TCP port numbers are not allowed for a MB_SERVER passive
connection: 20, 21, 25, 80, 102, 123, 5001, 34962, 34963, and 34964.
Variant
Pointer to the MB_SERVER Modbus holding register: The holding register
must either be a standard global DB or a M memory address. This memory
area is used to hold the values a Modbus client is allowed to access using
Modbus register functions 3 (read), 6 (write), and 16 (write).
Bool
New Data Ready: 0 = No new data, 1 = Indicates that new data has been
written by a Modbus client
Bool
Data Read: 0 = No data read, 1 = Indicates that data has been read by a
Modbus client.
Bool
The ERROR bit is TRUE for one scan, after MB_SERVER execution was
terminated with an error. The error code value at the STATUS parameter is
valid only during the single cycle where ERROR = TRUE.
Word
Execution condition code
Modbus functions
Data area
Address range
Output
1
Input
10001
30001
Output
1
Output
1
Communication processor and Modbus TCP
Data area
To
8192
Output Process Image
To
18192
Input Process Image
To
30512
Input Process Image
To
8192
Output Process Image
To
8192
Output Process Image
12.5 Modbus communication
S7-1200
CPU address
Q0.0 to Q1023.7
I0.0 to I1023.7
IW0 to IW1022
Q0.0 to Q1023.7
Q0.0 to Q1023.7
737
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