Communication processor and Modbus TCP
13.5 Modbus communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1203
Modbus_Master instruction data block (DB) tags
The following table shows the public static tags stored in the Modbus_Master instance DB
that you can use in your program:
Table 13- 77 Modbus_Master instance DB static tags
Blocked_Proc_Timeout Real 0.5 Duration (in seconds) for which to wait for a blocked Modbus_Master
instance before this instance is removed as ACTIVE. This can occur,
for example, if a Modbus_Master request is issued and the program
then stops to call the Modbus_Master function before it has completely
finished the request. The time value must be greater than 0 and less
than 55 seconds, or an error occurs.
Extended_Addressing Bool FALSE Configures single or double-byte slave station addressing:
• FALSE = One-byte address; 0 to 247
• TRUE = Two-byte address (corresponds to extended addressing);
0 to 65535
MD_DB MB_BASE - The MB_DB parameter of the Modbus_Comm_Load instruction must
be connected to the MB_DB parameter of the Modbus_Master instruc-
Your program can write values to the Blocked_Proc_Timeout and Extended_Addressing
variables to control the Modbus_Master operations. See the MB_SLAVE topic description of
HR_Start_Offset and Extended_Addressing (Page 1206) for an example of how to use these
variables in the program editor and details about Modbus extended addressing.
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