1. IModbusMaster and its implementations now have Async versions of its methods which return Task:

   Task<bool[]> ReadCoilsAsync(byte slaveAddress, ushort startAddress, ushort numberOfPoints);
   Task<bool[]> ReadInputsAsync(byte slaveAddress, ushort startAddress, ushort numberOfPoints);
   Task<ushort[]> ReadHoldingRegistersAsync(byte slaveAddress, ushort startAddress, ushort numberOfPoints);
   Task<ushort[]> ReadInputRegistersAsync(byte slaveAddress, ushort startAddress, ushort numberOfPoints);
   Task WriteSingleCoilAsync(byte slaveAddress, ushort coilAddress, bool value);
   Task WriteSingleRegisterAsync(byte slaveAddress, ushort registerAddress, ushort value);
   Task WriteMultipleRegistersAsync(byte slaveAddress, ushort startAddress, ushort[] data);
   Task WriteMultipleCoilsAsync(byte slaveAddress, ushort startAddress, bool[] data);
   Task<ushort[]> ReadWriteMultipleRegistersAsync(byte slaveAddress, ushort startReadAddress, ushort numberOfPointsToRead, ushort startWriteAddress, ushort[] writeData);
   

2. Opposite to event ModbusSlaveRequestReceived added event WriteComplete which fired by slave after write operation completed.

Acknowledgements

@breyed