Equipments (Devices) > PLC200 > Program > Communication Network > Modbus TCP > MBTCP

Block that performs a reading of up to 64 16-bit registers (via Read Holding Registers or Read Input Registers) of a server on the Modbus TCP network.

Ladder Representation

MBTCP_READREGISTER_block

Block Structure

Variable Type	Name	Data Type	Description
VAR_INPUT	Execute	BOOL	Block enabling
	ServerAddress	DWORD	Server IP address (Ex: 192.168.0.1)
	ServerPort	WORD	Modbus TCP Port of the server (Standard: 502)
	UnitID	BYTE	UnitID do servidor (Standard: 255)
	Function#	BYTE	Reading function code
	InitialDataAddress	WORD	Initial register address to be read
	NumberOfData	BYTE	Number of registers to be read (1 to 64)
	Timeout#	WORD	Maximum waiting time for the server response [ms]
	Offset#	BOOL	Offset Indication in InitialDataAddress, i.e., need to subtract 1 from this number
VAR_OUTPUT	Done	BOOL	Output enabling
	Active	BOOL	Awaiting response flag
	Busy	BOOL	Flag indicating the connection is busy with another request
	Error	BOOL	Error in the execution flag
	ErrorID	BYTE	Identifier of the occurred error
	Value	BYTE SINT USINT WORD UINT INT DWORD UDINT DINT REAL	Variable that stores the received data
VAR	MBTCP_READREGISTER_INST_0	MBTCP_READREGISTER	Instance of access to block structure

Operation

When this block detects a leading edge on Execute, it checks whether the Modbus TCP server in specified address in ServerAddress is free to send data (Busy variable at FALSE level). If so, it sends the reading request of a number of registers indicated by NumberOfData in InitialDataAddress address using chosen function in Function# and sets the Active output, resetting it when receiving the response from the server. The received data is stored in the Value variable. If the server is not free, the block waits Busy go to FALSE level to resubmit the request.

NOTE!

If Execute goes to FALSE level and Busy is still at TRUE level, the request is canceled.

NOTE!

Value is an array of number of bits NumberOfData multiplied by 16. That is, if NumberOfData is 16, Value can be an array of 32 BYTE positions, 16 WORD positions or 8 DWORD positions. It is important to check this compatibility not to generate errors in the block.

When Execute has FALSE value, Done remains FALSE. The Done output is only activated when the block finishes executing successfully, remaining at TRUE level until Execute receives FALSE.

If there is any error in the execution, the Error output is enabled and ErrorID displays an error code according to the table below.

Code	Description
0	Executed successfully
1	Invalid input data
2	Client not enabled
4	Timeout in server response
5	Server returned error
6	Failed to connect to server
7	TCP/IP connection terminated prematurely

Compatibility

Device	Version
PLC300	1.30 or higher

Block Flowchart

MBTCP_READREGISTER_flowchart

Example in Ladder

MBTCP_READREGISTER_example01

The above example requests reading of a number of register data described by DATA_COUNT positioned in the INIT1 in Modbus TCP server of SERVER:PORT address through the Read Holding Register function. These data are forwarded to VALUE. 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

SERVER : DWORD := 16#C0A8000A; // 192.168.0.10 = 3232235530

PORT : WORD := 502;

UNITID : BYTE := 255;

INIT : WORD;

DATA_COUNT : BYTE;

VALUE : ARRAY [0..4] OF WORD;

MBTCP_READREGISTER_INST_0 : FB_MBTCP_ReadRegister;

END_VAR

MBTCP_READREGISTER_INST_0.Execute := DI1;

MBTCP_READREGISTER_INST_0(

ServerAddress:=SERVER,

ServerPort:=PORT,

UnitID:=UNITID,

Function:=3,

InitialDataAddress:=INIT,

NumberOfData:=DATA_COUNT,

Timeout:=50,

Offset:=0,

Value=>VALUE);

DO1 := MBTCP_READREGISTER_INST_0.Done;