Using Serial Protocols

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. Include the library header files

#include "MbusRtuMasterProtocol.hpp"

2. Device data profile definition

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

short readRegSet[20];
short writeRegSet[20];
int readBitSet[20];
int writeBitSet[20];

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

float readFloatSet[10];

float writeFloatSet[10];

Note that because a float occupies two 16-bit registers the array size is half the size it would be for 16-bit shorts!

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

long readLongSet[10];

long writeLongSet[10];

Note that because a long occupies two 16-bit registers the array size is half the size it would be for 16-bit shorts!

3. Declare and instantiate a protocol object

MbusRtuMasterProtocol mbusProtocol;

4. Open the protocol

int result;
result = mbusProtocol.openProtocol(portName,
                                   19200L, // Baudrate
                                   8,      // Databits
                                   1,      // Stopbits
                                   2);     // Even parity
if (result != FTALK_SUCCESS)
{
   fprintf(stderr, "Error opening protocol: %s!\n",
                    getBusProtocolErrorText(result));
   exit(EXIT_FAILURE);
}

5. Perform the data transfer functions

To read register values:
mbusProtocol.readMultipleRegisters(1, 100, readRegSet,
sizeof(readRegSet) / sizeof(short));
To write a single register value:
mbusProtocol.writeSingleRegister(1, 200, 1234);
To write mutliple register values:
mbusProtocol.writeMultipleRegisters(1, 200, writeRegSet,
sizeof(writeRegSet) / sizeof(short));
To read discrete values:
mbusProtocol.readCoils(1, 10, readBitSet, sizeof(readBitSet) / sizeof(int));
To write a single discrete value:
mbusProtocol.writeCoil(1, 20, 1);
To write multiple discrete values:
mbusProtocol.forceMultipleCoils(1, 20, sizeof(writeBitSet) / sizeof(int));
To read float values:
mbusProtocol.readMultipleFloats(1, 100, readFloatSet,
sizeof(readFloatSet) / sizeof(float));
To read long integer values:
mbusProtocol.readMultipleLongInts(1, 100, readLongSet,
sizeof(readLongSet) / sizeof(long));

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 return an error code. The following code snippet can handle and report these errors:

int result;
result = mbusProtocol.readMultipleRegisters(1, 100, dataSetArray, 10);
if (result != FTALK_SUCCESS)
{
   fprintf(stderr, "%s!\n", getBusProtocolErrorText(result));
   // Stop for fatal errors
   if (!(result & FTALK_BUS_PROTOCOL_ERROR_CLASS))
      return;
}

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.

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. Include the library header files

#include "MbusTcpMasterProtocol.hpp"

2. Device data profile definition

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

short readRegSet[20];
short writeRegSet[20];
int readBitSet[10];
int writeBitSet[10];

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

float readFloatSet[10];

float writeFloatSet[10];

Note that because a float occupies two 16-bit registers the array size is half the size it would be for 16-bit shorts!

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

long readLongSet[10];

long writeLongSet[10];

Note that because a long occupies two 16-bit registers the array size is half the size it would be for 16-bit shorts!

3. Declare and instantiate a protocol object

MbusTcpMasterProtocol mbusProtocol;

4. Open the protocol

mbusProtocol.openProtocol("10.0.0.11");

5. Perform the data transfer functions

To read register values:
mbusProtocol.readMultipleRegisters(1, 100, readRegSet,
sizeof(readRegSet) / sizeof(short));
To write a single register value:
mbusProtocol.writeSingleRegister(1, 200, 1234);
To write mutliple register values:
mbusProtocol.writeMultipleRegisters(1, 200, writeRegSet,
sizeof(writeRegSet) / sizeof(short));
To read discrete values:
mbusProtocol.readCoils(1, 10, readBitSet, sizeof(readBitSet) / sizeof(int));
To write a single discrete value:
mbusProtocol.writeCoil(1, 20, 1);
To write multiple discrete values:
mbusProtocol.forceMultipleCoils(1, 20, writeBitSet,
sizeof(writeBitSet) / sizeof(int));
To read float values:
mbusProtocol.readMultipleFloats(1, 100, readFloatSet,
sizeof(readFloatSet) / sizeof(float));
To read long integer values:
mbusProtocol.readMultipleLongInts(1, 100, readLongSet,
sizeof(readLongSet) / sizeof(long));

6. Close the connection if not needed any more

mbusProtocol.closeProtocol();

7. Error Handling

TCP/IP protocol errors like slave failures, TCP/IP connection failures and time-outs return an error code. The following code snippet can handle these errors:

int result;
result = mbusProtocol.readMultipleRegisters(1, 100, dataSetArray, 10);
if (result != FTALK_SUCCESS)
{
   fprintf(stderr, "%s!\n", getBusProtocolErrorText(result));
   // Stop for fatal errors
   if (!(result & FTALK_BUS_PROTOCOL_ERROR_CLASS))
      return;
}

If the method returns FTALK_CONNECTION_WAS_CLOSED, it signals that the the TCP/IP connection was lost or closed by the remote end. Before using further data and control functions the connection has to be re-opened succesfully.