Denilson Pegaia

Hi,

Here there are some tips and tricks related to MODBUS RTU communication with S7-1500:

References:

Manual: http://support.automation.siemens.com/WW/view/en/59057093
Complete sample program: http://support.automation.siemens.com/BR/view/en/68202723

Requirements:

To establish a MODBUS RTU communication it is necessary a High Feature Comunication Module, (not Basic )

HW configuration:

Device View, Communication Module properties, Port Configuration, Protocol: set to MODBUS

Programming:

Blocks needed:
As master: Modbus_Comm_Load / Modbus_Master
As slave: Modbus_Comm_Load / Modbus_Slave

Call: call both block unconditionally

REQ:
Modbus_Comm_Load: use first scan bit
Modbus_Master: should be set (0->1) every time you need to execute a job. My tip: use a 1s clock for the first tests, it slow enough to be observed by eye. When functional, you can change it for a faster clock (e.g. 100ms).

Modbus_Comm_Load parameters:
e.g. follow the online help.
MB_DB: should be connected to the variable MB_DB from the instance DB of the blocks

Mode: Mode is not an external parameter but else an internal FB variable. It should be set to the operation mode (see online help; e.g. RS232=0, 485=4) before the call the Modbus_Comm_Load.

Other communication parameters:
MODBUS RTU uses 1 startbits, 8 databits, 1 Stopbit (up to now, not configurable).

Here there is a very simple non tested sample program (the complete version is related above).

 Hello Pegaia,

I have V14 SP1 and trying to communicate Schneider energy meter EM6400 with S7-1500 on Modbus

I am not able to communicate and getting error code 8283

Energy meter and PLC configuration Modbus settings are same ie baud rate  9600. stop bit 1, parity even and data bits 8

As I want to read holding registers from EM6400,

I moved 4 in "ModbusCommunicationLoad_db".Mode

and 0 in Modbus master block Mode input.

Data adder for Modbus master is 43915 to read frequency

data length 4

and data ptr is P#DB3.DBX0.0 BYTE 8

wher DB3 Is a data blcock with array of int having size of int0 to int 100

please help me to resolve.

Thank you,

Damayanti

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Split from TIPs: S7-1500 – MODBUS RTU.

Hi,

problem resolved. Actually energy meter is EM6400NG. We were trying with holding register address for EM6400.

Thank you.

Damayanti