Communication processor and Modbus TCP
13.5 Modbus communication
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1197
Modbus_Comm_Load instance data block (DB) tags
The following table shows the public static tags stored in the Modbus_Comm_Load instance
DB that can be used in your program:
Table 13- 72 Modbus_Comm_Load instance DB static tags
ICHAR_GAP Word 0 Maximum character delay time between characters. This parameter is
specified in milliseconds and increases the anticipated period between
the received characters. The corresponding number of bit times for this
parameter is added to the Modbus default value of 35 bit times (3.5
RETRIES Word 2 Number of retries that the master executes before the error code
0x80C8 for "No response" is returned.
Enable diagnostics for missing supply voltage L+.
MODE USInt 0 Operating mode
Valid operating modes are as follows:
• 0 = Full duplex (RS232)
• 1 = Full duplex (RS422) four-wire mode (point-to-point)
• 2 = Full duplex (RS422) four-wire mode (multipoint master, CM PtP
(ET 200SP))
• 3 = Full duplex (RS422) four-wire mode (multipoint slave, CM PtP
(ET 200SP))
• 4 = Half duplex (RS485) two-wire mode (See Note below.)
LINE_PRE USInt 0 Receive line initial state
Valid initial states are as follows:
• 0 = "No" initial state (See Note below.)
• 1 = signal R(A) = 5 V DC, signal R(B) = 0 V DC (break detection):
Break detection is possible with this initial state.
Can only be selected with: "Full duplex (RS422) four-wire mode
(point-to-point connection)" and "Full duplex (RS422) four-wire
mode (multipoint slave)".
• 2 = signal R(A) = 0 V DC, signal R(B) = 5 V DC:
This default setting corresponds to the idle state (no active send
operation). No break detection is possible with this initial state.
BRK_DET USInt 0 Break detection
The following selections are valid:
• 0 = break detection deactivated
• 1 = break detection activated
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