Method ModbusMasterTransaction

src/ModbusMaster.cpp:600–876

_____PRIVATE FUNCTIONS____________________________________________________ */ Modbus transaction engine. Sequence: - assemble Modbus Request Application Data Unit (ADU), based on particular function called - transmit request over selected serial port - wait for/retrieve response - evaluate/disassemble response - return status (success/exception) @param u8MBFunction Modbus function (

@return 0 on success; exception number on failure
*/
uint8_t ModbusMaster::ModbusMasterTransaction(uint8_t u8MBFunction)
{
  uint8_t u8ModbusADU[256];
  uint8_t u8ModbusADUSize = 0;
  uint8_t i, u8Qty;
  uint16_t u16CRC;
  uint32_t u32StartTime;
  uint8_t u8BytesLeft = 8;
  uint8_t u8MBStatus = ku8MBSuccess;
  
  // assemble Modbus Request Application Data Unit
  u8ModbusADU[u8ModbusADUSize++] = _u8MBSlave;
  u8ModbusADU[u8ModbusADUSize++] = u8MBFunction;
  
  switch(u8MBFunction)
  {
    case ku8MBReadCoils:
    case ku8MBReadDiscreteInputs:
    case ku8MBReadInputRegisters:
    case ku8MBReadHoldingRegisters:
    case ku8MBReadWriteMultipleRegisters:
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16ReadAddress);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16ReadAddress);
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16ReadQty);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16ReadQty);
      break;
  }
  
  switch(u8MBFunction)
  {
    case ku8MBWriteSingleCoil:
    case ku8MBMaskWriteRegister:
    case ku8MBWriteMultipleCoils:
    case ku8MBWriteSingleRegister:
    case ku8MBWriteMultipleRegisters:
    case ku8MBReadWriteMultipleRegisters:
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16WriteAddress);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16WriteAddress);
      break;
  }
  
  switch(u8MBFunction)
  {
    case ku8MBWriteSingleCoil:
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16WriteQty);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16WriteQty);
      break;
      
    case ku8MBWriteSingleRegister:
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16TransmitBuffer[0]);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16TransmitBuffer[0]);
      break;
      
    case ku8MBWriteMultipleCoils:
      u8ModbusADU[u8ModbusADUSize++] = highByte(_u16WriteQty);
      u8ModbusADU[u8ModbusADUSize++] = lowByte(_u16WriteQty);
      u8Qty = (_u16WriteQty % 8) ? ((_u16WriteQty >> 3) + 1) : (_u16WriteQty >> 3);
      u8ModbusADU[u8ModbusADUSize++] = u8Qty;