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

Block that allows monitoring the status of 4 slaves of the Modbus RTU network.

Ladder Representation

MB_SLAVESTATUS_block

Block Structure

Variable Type	Name	Data Type	Description
VAR_INPUT	Execute	BOOL	Block enabling
	ErrorsToSetOffline#	BYTE	Amount of errors that the master must identify until it considers communication with an offline slave
	AddressSlave1#	BYTE	Slave address 1 to be monitored
	AddressSlave2#	BYTE	Slave address 2 to be monitored
	AddressSlave3#	BYTE	Slave address 3 to be monitored
	AddressSlave4#	BYTE	Slave address 4 to be monitored
VAR_OUTPUT	Done	BOOL	Output enabling
	GeneralOffline	BOOL	Flag indicating any one of the monitored communication is offline
	Slave1Offline	BOOL	Flag of offline status slave 1
	Slave2Offline	BOOL	Flag of offline status slave 2
	Slave3Offline	BOOL	Flag of offline status slave 3
	Slave4Offline	BOOL	Flag of offline status slave 4

Operation

This block remains active while Execute is at TRUE level, updating its outputs according to the number of errors recorded for each slave. 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.

The ErrorsToSetOffline # input allows registering the number of errors identified in a slave that will feature an offline communication. AddressSlave inputs allow inserting four slave addresses to be monitored. When this monitored slave reports the programmed number of errors, its corresponding SlaveOffline output is set to TRUE level. If any of SlaveOffline outputs is at TRUE level, GeneralOffline also receives TRUE level.

Block Flowchart

MB_SLAVESTATUS_flowchart

Example in Ladder

MB_SLAVESTATUS_example01

The above example checks the number of error responses sent by the slaves 2, 4, 6 and 8 of the Modbus RTU. If any of them is greater than 5, its SX_OFF status is led to TRUE level. 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

ANY_OFFLINE, S1_OFF, S2_OFF, S3_OFF, S4_OFF : BOOL;

END_VAR

DO1 := FB_MB_SlaveStatus(

Execute:=DI1,

ErrorsToSetOffline:=5,

AddressSlave1:=2,

AddressSlave2:=4,

AddressSlave3:=6,

AddressSlave4:=8,

GeneralOffline=>ANY_OFFLINE,

Slave1Offline=>S1_OFF,

Slave2Offline=>S2_OFF,

Slave3Offline=>S3_OFF,

Slave4Offline=>S4_OFF);