Siemens SIMATIC S7-1200 System Manual page 1197

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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

EN_SUPPLY_VOLT

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK

Communication processor and Modbus TCP

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

character times).

Number of retries that the master executes before the error code

0x80C8 for "No response" is returned.

Enable diagnostics for missing supply voltage L+.

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

3 = Full duplex (RS422) four-wire mode (multipoint slave, CM PtP

4 = Half duplex (RS485) two-wire mode (See Note below.)

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.

Break detection

The following selections are valid:

0 = break detection deactivated

1 = break detection activated

13.5 Modbus communication

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