Equipments (Devices) > CFW500 > Ladder > Communication Network > Modbus RTU > MB

Block that allows monitoring various statuses of the Modbus RTU network master.

Ladder Representation

MB_MASTERCONTROLSTATUS_block

Block Structure

Variable Type	Name	Data Type	Description
VAR_INPUT	Execute	BOOL	Block enabling
VAR_INPUT	DisableComm	BOOL	Disables Modbus RTU communication
VAR_OUTPUT	Done	BOOL	Output enabling
	CommDisabled	BOOL	Disabled communication flag
	TxCounter	WORD UINT	Counter of requests sent
	RxCounter	WORD UINT	Counter of telegrams received
	NoAnswerCounter	WORD UINT	Counter of requests not answered
	ErrorResponseCounter	WORD UINT	Counter of responses received with error information
	LastErrorSlaveAddress	BYTE USINT	Slave address in which the last communication error was detected
	LastErrorResult	BYTE USINT	Operation result of the last communication error received (0 = No error) (4 – Response Timeout) (5 = Slave returned error)
	LastErrorCode	BYTE USINT	Code of the last communication error received

Operation

This block remains active while Execute is at TRUE level, updating its outputs according to the monitoring of the master and input requests. When Execute receives FALSE level, the inputs are ignored and the outputs are zeroed. The Done output receives TRUE level when Execute has TRUE level and block finished its execution.

A TRUE level DisableComm disables the Modbus RTU communication and resets the status counters and markers of the master. These markers and counters are displayed in the output block each having some data corresponding to its description. Their values are also cleared at shutdown of the master.

Block Flowchart

MB_MASTERCONTROLSTATUS_flowchart

Example in Ladder

MB_MASTERCONTROLSTATUS_example01

The example above requests status data of the Modbus RTU network master, and allows disabling communication through DISABLE. The block ends successfully, Done output is activated.

Example in ST

The example below displays the instructions for applying the example above in the ST language.

VAR

DISABLE, MB_DISABLE : BOOL;

COUNT_TX, COUNT_RX, COUNT_NOANSWER, COUNT_ERROR : WORD;

LE_ADDRESS, LE_RESULT, LE_CODE : USINT;

END_VAR

DO1 := FB_MB_MasterControlStatus(

DisableComm:=DISABLE,

Execute:=DI1,

CommDisabled=>MB_DISABLE,

TxCounter=>COUNT_TX,

RxCounter=>COUNT_RX,

NoAnswerCounter=>COUNT_NOANSWER,

ErrorResponseCounter=>COUNT_ERROR,

LastErrorSlaveAddress=>LE_ADDRESS,

LastErrorResult=>LE_RESULT,

LastErrorCode=>LE_CODE);