This class realises the server-side of the Modbus RTU slave protocol. More...

Public Types
enum	{ SER_DATABITS_7 = 7, SER_DATABITS_8 = 8 }

enum	{ SER_STOPBITS_1 = 1, SER_STOPBITS_2 = 2 }

enum	{ SER_PARITY_NONE = 0, SER_PARITY_EVEN = 2, SER_PARITY_ODD = 1 }

Public Member Functions
	MbusRtuSlaveProtocol ()
	Instantiates a Modbus RTU protocol server object. More...

int	startupServer (const TCHAR *const portName, long baudRate, int dataBits, int stopBits, int parity)
	Puts the Modbus RTU server into operation and opens the associated serial port with specific port parameters. More...

int	serverLoop ()
	Modbus slave server loop. More...

int	setFrameTolerance (long frameToleranceMs)
	Configures the tolerance the RTU protocol engine should apply for the detection of inter-frame gaps. More...

void	shutdownServer ()
	Shuts down the Modbus server. More...

int	isStarted ()
	Returns whether server has been started up. More...

virtual int	enableRs485Mode (int rtsDelay)
	Enables RS485 mode. More...

int	addDataTable (int slaveAddr, MbusDataTableInterface *dataTablePtr)
	Associates a protocol object with a Data Provider and a Modbus slave ID. More...

int	getConnectionStatus ()
	Checks if a Modbus master is polling periodically. More...

Static Public Member Functions
static const TCHAR *	getPackageVersion ()
	Returns the library version number. More...

Protocol Configuration
int	setTimeout (long timeOut)
	Configures master activity time-out supervision. More...

long	getTimeout ()
	Returns the currently set master activity time-out value. More...

void	disableExceptionReplies ()
	Supress exception replies to be sent. More...

void	enableExceptionReplies ()
	Enables exception replies after they have been turned off. More...

Transmission Statistic Functions
unsigned long	getTotalCounter ()
	Returns how often a message transfer has been executed. More...

void	resetTotalCounter ()
	Resets total message transfer counter.

unsigned long	getSuccessCounter ()
	Returns how often a message transfer was successful. More...

void	resetSuccessCounter ()
	Resets successful message transfer counter.

Detailed Description

This class realises the server-side of the Modbus RTU slave protocol.

It provides functions to start-up and to execute the server engine which includes opening and closing of the serial port. Upon receipt of a valid master query the server engine calls Data Provider methods to exchange data with the user application. For a more detailed description which Modbus data and control functions have been implemented in the server engine see section Server Functions common to all Modbus Protocol Flavours.

It is possible to instantiate multiple instances for establishing multiple connections on different serial ports, however they must be executed in separate threads.

See also: Server Functions common to all Modbus Protocol Flavours, Serial Protocols; MbusDataTableInterface, MbusAsciiSlaveProtocol, MbusTcpSlaveProtocol

Member Enumeration Documentation

◆ anonymous enum

anonymous enum

inherited

Enumerator
SER_DATABITS_7	7 data bits
SER_DATABITS_8	8 data bits

◆ anonymous enum

anonymous enum

inherited

Enumerator
SER_STOPBITS_1	1 stop bit
SER_STOPBITS_2	2 stop bits

◆ anonymous enum

anonymous enum

inherited

Enumerator
SER_PARITY_NONE	No parity.
SER_PARITY_EVEN	Even parity.
SER_PARITY_ODD	Odd parity.

Constructor & Destructor Documentation

◆ MbusRtuSlaveProtocol()

MbusRtuSlaveProtocol ( )

Instantiates a Modbus RTU protocol server object.

The association with a Data Provider is done after construction using the addDataTable method.

References MasterInfo::protocol, and MasterInfo::RTU.

Member Function Documentation

◆ startupServer()

int startupServer	(	const TCHAR *const	portName,
		long	baudRate,
		int	dataBits,
		int	stopBits,
		int	parity
	)

virtual

Puts the Modbus RTU server into operation and opens the associated serial port with specific port parameters.

This function opens the serial port and initialises the server engine.

Parameters

portName	Serial port identifier (e.g. "COM1", "/dev/ser1" or "/dev/ttyS0")
baudRate	The port baudRate in bps (typically 1200 - 115200, maximum value depends on UART hardware)
dataBits	Must be SER_DATABITS_8 for RTU
stopBits	SER_STOPBITS_1: 1 stop bit, SER_STOPBITS_2: 2 stop bits
parity	SER_PARITY_NONE: no parity, SER_PARITY_ODD: odd parity, SER_PARITY_EVEN: even parity

Note: The Modbus standard requires two stop bits if no parity is chosen. This library is not enforcing this but it is a recommended configuration.

Returns: FTALK_SUCCESS on success or error code. See Error Management for a list of error codes.

Reimplemented from MbusSerialServerBase.

References FTALK_ILLEGAL_ARGUMENT_ERROR, MbusSerialServerBase::SER_DATABITS_8, and MbusSerialServerBase::startupServer().

◆ serverLoop()

int serverLoop ( )

virtual

Modbus slave server loop.

This server loop must be called continuously. It must not be blocked. The server has to be started before calling the serverLoop() method.

In most cases the server loop is executed in an infinite loop in its own thread:

while (notTerminated) {
  mbusProtocol.serverLoop();
}

Returns: FTALK_SUCCESS on success or error code. See Error Management for a list of error codes.

Implements MbusSlaveServer.

References FTALK_IO_ERROR, and FTALK_SUCCESS.

◆ setFrameTolerance()

int setFrameTolerance ( long frameToleranceMs )

Configures the tolerance the RTU protocol engine should apply for the detection of inter-frame gaps.

Modbus RTU uses inter-frame gaps (silence periods) to mark start and end of Modbus packets.

Warning: For strict Modbus compliance this should be set to 0.

Remarks: There are cases were longer silence periods may appear in the data stream due to the hardware used (USB dongles) or the device driver or the scheduling of the operating system. This value can then be increased to compensate. In a point-to-point communication system (eg RS-232) this value can be safley increased. However in a multi-point system were other slave devices are on the line, this value should be set to the lowest possible value in order to maintain interoperability with other Modbus equipment.

Note: A protocol must be closed in order to configure it.

Parameters

frameToleranceMs Additional tolerance time for inter-frame silence detection in ms (Range: 0 - 20)

Return values

FTALK_SUCCESS	Success
FTALK_ILLEGAL_ARGUMENT_ERROR	Argument out of range

References FTALK_ILLEGAL_ARGUMENT_ERROR, FTALK_ILLEGAL_STATE_ERROR, FTALK_SUCCESS, and MbusSerialServerBase::isStarted().

◆ shutdownServer()

void shutdownServer ( )

virtualinherited

Shuts down the Modbus server.

This function also closes any associated communication resources like serial ports or sockets.

Implements MbusSlaveServer.

◆ isStarted()

int isStarted ( )

virtualinherited

Returns whether server has been started up.

Return values

true	= started
false	= shutdown

Implements MbusSlaveServer.

◆ enableRs485Mode()

int enableRs485Mode ( int rtsDelay )

virtualinherited

Enables RS485 mode.

In RS485 mode the RTS signal can be used to enable and disable the transmitter of a RS232/RS485 converter. The RTS signal is asserted before sending data. It is cleared after the transmit buffer has been emptied and in addition the specified delay time has elapsed. The delay time is necessary because even the transmit buffer is already empty, the UART's FIFO will still contain unsent characters.

Warning: The use of RTS controlled RS232/RS485 converters should be avoided if possible. It is difficult to determine the exact time when to switch off the transmitter with non real-time operating systems like Windows and Linux. If it is switched off to early characters might still sit in the FIFO or the transmit register of the UART and these characters will be lost. Hence the slave will not recognize the message. On the other hand if it is switched off too late then the slave's message is corrupted and the master will not recognize the message.

Remarks: The delay value is indicative only and not guaranteed to be maintained. How precise it is followed depends on the operating system used, it's scheduling priority and it's system timer resolution.

Note: This mode must be set before starting the server in order to come into effect.

Parameters

rtsDelay Delay time in ms (Range: 0 - 100000) which applies after the transmit buffer is empty. 0 disables this mode.

Return values

FTALK_SUCCESS	Success
FTALK_ILLEGAL_ARGUMENT_ERROR	Argument out of range
FTALK_ILLEGAL_STATE_ERROR	Protocol is already open

References FTALK_ILLEGAL_ARGUMENT_ERROR, FTALK_ILLEGAL_STATE_ERROR, FTALK_SUCCESS, and MbusSerialServerBase::isStarted().

◆ addDataTable()

int addDataTable	(	int	slaveAddr,
		MbusDataTableInterface *	dataTablePtr
	)

inherited

Associates a protocol object with a Data Provider and a Modbus slave ID.

Parameters

slaveAddr	Modbus slave address for server to listen on (-1 - 255). 0 is regarded as a valid value for a MODBUS/TCP server address. A value of -1 means the server disregards the slave address and listens to all slave addresses. 0 or -1 is only valid for MODBUS/TCP!
dataTablePtr	Modbus data table pointer. Must point to a Data Provider object derived from the MbusDataTableInterface class. The Data Provider is the interface between your application data and the Modbus network.

Returns: FTALK_SUCCESS on success or error code. See Error Management for a list of error codes.

References FTALK_ILLEGAL_ARGUMENT_ERROR, and FTALK_SUCCESS.

◆ getConnectionStatus()

int getConnectionStatus ( )

inlineinherited

Checks if a Modbus master is polling periodically.

Return values

true	= A master is polling at a frequency higher than the master transmit time-out value
false	= No master is polling within the time-out period

Note: The master transmit time-out value must be set > 0 in order for this function to work.

◆ setTimeout()

int setTimeout ( long timeOut )

inherited

Configures master activity time-out supervision.

The slave can monitor whether a master is actually polling or not. This function sets the activity time-out to the specified value. A value of 0 disables the time-out, which stops time-out notifications being sent to the Data Provider. Default value is 1000 ms.

Remarks: The time-out value is a minimum value only and the actual time may be longer. How precise it is followed depends on the operating system used, its scheduling priority and its system timer resolution.

Note: The time-out does not check whether a master is sending valid frames. The transmission of characters is sufficient to avoid the time-out.

Parameters

timeOut Timeout value in ms (Range: 0 - 100000), 0 disables time-out

Return values

FTALK_SUCCESS	Success
FTALK_ILLEGAL_ARGUMENT_ERROR	Argument out of range

References FTALK_ILLEGAL_ARGUMENT_ERROR, and FTALK_SUCCESS.

◆ getTimeout()

long getTimeout ( )

inlineinherited

Returns the currently set master activity time-out value.

Returns: Timeout value in ms

◆ disableExceptionReplies()

void disableExceptionReplies ( )

inherited

Supress exception replies to be sent.

With this option only positive replies are sent to the master. All failure replies are silently discarded. This option can be useful if redundant Modbus devices are used. In this scenario supressing the reply would trigger a swap-over of the redundant devices.

◆ enableExceptionReplies()

void enableExceptionReplies ( )

inherited

Enables exception replies after they have been turned off.

Sending exception replies in case of slave failures is the normal mode of operation.

◆ getTotalCounter()

unsigned long getTotalCounter ( )

inlineinherited

Returns how often a message transfer has been executed.

Returns: Counter value

◆ getSuccessCounter()

unsigned long getSuccessCounter ( )

inlineinherited

Returns how often a message transfer was successful.

Returns: Counter value

◆ getPackageVersion()

const TCHAR * getPackageVersion ( )

staticinherited

Returns the library version number.

Returns: Version string

Public Types

Public Member Functions

Static Public Member Functions

Protocol Configuration

Transmission Statistic Functions

Detailed Description

Member Enumeration Documentation

◆ anonymous enum

◆ anonymous enum

◆ anonymous enum

Constructor & Destructor Documentation

◆ MbusRtuSlaveProtocol()

Member Function Documentation

◆ startupServer()

◆ serverLoop()

◆ setFrameTolerance()

◆ shutdownServer()

◆ isStarted()

◆ enableRs485Mode()

◆ addDataTable()

◆ getConnectionStatus()

◆ setTimeout()

◆ getTimeout()

◆ disableExceptionReplies()

◆ enableExceptionReplies()

◆ getTotalCounter()

◆ getSuccessCounter()

◆ getPackageVersion()