net.sourceforge.jmodbus
Class ModbusASCIITransport

java.lang.Object
  |
  +--net.sourceforge.jmodbus.ModbusASCIITransport

All Implemented Interfaces:

ModbusTransport

public class ModbusASCIITransport

extends java.lang.Object

implements ModbusTransport

Class to implement a ASCII transport mechanisim for Modbus communication. This will allow a decice to communicate a serial link, using ASCII encoding of the data.

Field Summary

static byte	END_FRAME_MARKER_1 The first character of the end of frame marker for Modbus ASCII messages.
static byte	END_FRAME_MARKER_2 The first character of the end of frame marker for Modbus ASCII messages.
static int	MAX_ASCII_MESSAGE_LENGTH The maximum length of a Modbus ASCII message that is based on the maximum length of a Modbus message, with 2 characters per byte encoding and start and end delimiters.
static byte	START_FRAME_MARKER The start of frame marker for Modbus ASCII messages.

Constructor Summary

ModbusASCIITransport()
Default constructor that will create it's own serial port connection with the default port settings.

ModbusASCIITransport(javax.comm.SerialPort port)
Constructor that passes a open serial port.

Method Summary

boolean	receiveFrame(ModbusMessage msg) Method to receive a Modbus frame via the transport media.
boolean	sendFrame(ModbusMessage msg) Method to send a Modbus frame via the transport media.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

START_FRAME_MARKER

public static final byte START_FRAME_MARKER

The start of frame marker for Modbus ASCII messages.

END_FRAME_MARKER_1

public static final byte END_FRAME_MARKER_1

The first character of the end of frame marker for Modbus ASCII messages.

END_FRAME_MARKER_2

public static final byte END_FRAME_MARKER_2

The first character of the end of frame marker for Modbus ASCII messages.

MAX_ASCII_MESSAGE_LENGTH

public static final int MAX_ASCII_MESSAGE_LENGTH

The maximum length of a Modbus ASCII message that is based on the maximum length of a Modbus message, with 2 characters per byte encoding and start and end delimiters.

1. start delimeter (1 byte)
2. message body (2 * MAX_MESSAGE_LENGTH bytes)
3. LRC (2 bytes)
4. CR LF (2 bytes)

Constructor Detail

ModbusASCIITransport

public ModbusASCIITransport()

Default constructor that will create it's own serial port connection with the default port settings.

ModbusASCIITransport

public ModbusASCIITransport(javax.comm.SerialPort port)

Constructor that passes a open serial port. The serial port may have any parameters, but must alredy be opened, ready for communication.

Parameters:

port - The serial port to conduct serial communications over.

Method Detail

sendFrame

public boolean sendFrame(ModbusMessage msg)

Method to send a Modbus frame via the transport media. The return status of the function indicates if the transmission sucedded.

Specified by:

sendFrame in interface ModbusTransport

Parameters:

msg - The Modbus Message to be sent.

Returns:

Transmission sucess flag, to indicate if the transmission was sucessful.

receiveFrame

public boolean receiveFrame(ModbusMessage msg)

Method to receive a Modbus frame via the transport media. The return value indicates the length of the frame. This method will block until the comminication path is terminated or a frame is sucessfully received.

Even if false is return the Modbus Message that is passed may be modified. It's buffer is used to save excessive array copying.

Specified by:

receiveFrame in interface ModbusTransport

Parameters:

msg - The Modbus Message object for received data to be written into

Returns:

Receive sucess flag, to indicate if the receive was sucessful.