Let's assume we want to talk to a Modbus slave device with slave address 1.

The registers for reading are in the reference range 4:00100 to 4:00119 and the registers for writing are in the range 4:00200 to 4:00219. The discretes for reading are in the reference range 0:00010 to 0:00019 and the discretes for writing are in the range 0:00020 to 0:00029.

1. Import the library packages

uses
   MbusRtuMasterProtocol,
   BusProtocolExceptions;

2. Device data profile definition

Define the data sets which reflects the slave's data profile by type and size:

var
   readRegSet: array[1..20] of word;
   writeRegSet: array[1..10] of word;
   readBitSet: array[1..10] of boolean;
   writeBitSet: array[1..10] of boolean;

If you are using floats instead of 16-bit words define:

var
   readFloatSet: array[1..10] of single;
   writeFloatSet: array[1..10] of single;

If you are using 32-bit ints instead of 16-bit words define:

var
   readLongSet: array[1..10] of integer;
   writeLongSet: array[1..10] of integer;

3. Declare and instantiate a protocol object

var
   TMbusRtuMasterProtocol mbusProtocol;

4. Instantiate and open the protocol

   try
      mbusProtocol := TMbusRtuMasterProtocol.Create(nil);
      mbusProtocol.portName := 'COM1';
      mbusProtocol.baudRate := 9600;
      mbusProtocol.openProtocol;
   except
      on e: Exception do
      begin
         writeln('Error opening protocol: ', e.message, '!');
         halt(1);
      end;
   end;

5. Perform the data transfer functions

To read register values:

mbusProtocol.readMultipleRegisters(1, 100, readRegSet);

To write a single register value:

mbusProtocol.writeSingleRegister(1, 200, 1234);

To write mutliple register values:

mbusProtocol.writeMultipleRegisters(1, 200, writeRegSet);

To read discrete values:

mbusProtocol.readCoils(1, 10, readBitSet);

To write a single discrete value:
```
mbusProtocol.writeCoil(1, 20, true);
```

To write multiple discrete values:

mbusProtocol.forceMultipleCoils(1, 20, writeBitSet);

To read float values:

mbusProtocol.readMultipleFloats(1, 100, readFloatSet);

To read long integer values:

mbusProtocol.readMultipleLongInts(1, 100, readLongSet);

6. Close the protocol port if not needed any more

mbusProtocol.closeProtocol;

7. Error Handling

Serial protocol errors like slave device failures, transmission failures, checksum errors and time-outs throw an exception. The following code snippet can handle and report these errors:

      try
         mbusProtocol.readMultipleRegisters(1, 100, dataSetArray);
      except
         on e: EBusProtocolException do
            writeln(e.message, '!');
         on e: Exception do
         begin
            writeln('Fatal error: ', e.message, '!');
            halt(1);
         end;
      end;

An automatic retry mechanism is available and can be enabled with mbusProtocol.setRetryCnt(3) before opening the protocol port.

Using MODBUS/TCP Protocol

Let's assume we want to talk to a Modbus slave device with unit address 1 and IP address 10.0.0.11.

1. Import the library package

uses
   MbusTcpMasterProtocol,
   BusProtocolExceptions;