ServerTCP_extended (FB)¶

“wide registers” and endianess¶

The MODBUS standard defines the length of input / holding registers to read/write with 16-bit - no way out of this. The message definitions in the MODBUS standard come with some room for non-standard interpretation. FC03 Read Holding Registers should be used as an example here:

Request: Quantity of Registers Response: Byte count

So a non-standard MODBUS server can inform a client in the response indirectly about the register width (Response:Byte count = Request:Quantity of Registers * register width in Bytes). This fact leaded some vendors to implement MODBUS devices with registers > 16bit. Because the CODESYS ModbusFB lib should be usable with such non-standard devices (clients as well as servers) there is a Server*_extended and some related ClientRequest*RegistersWide in this library. Following client requests can be used with “wide registers”: - Read Holding Registers - Read Input Registers - Write Multiple registers - Read/Write Multiple registers

Following client requests can not be used with “wide registers” because of their MODBUS protocol data unit (PDU) definition: - Write Single Register - Mask Write Register because the “data item” width is explicitly defined to be 16bit.

A standard MODBUS client requesting register data from such a non-standard MODBUS server, unfortunately requesting register data from a register > 16bit gets confronted with an invalid Response: Byte count <> Quantity of Registers * 2, and will most likely drop such a response as invalid or less likely put out error/warning/information on this fact.

The MODBUS standard defines byte ordering in MODBUS messages to read/write 16-bit registers. The MODBUS standard doesnt define anything beyond this - so there is no rule for byte ordering in “wide registers”. This ServerTCP_extended is using the same byte ordering for register data > 16bit as defined in the MODBUS standard (“big-Endian” representation). So for example register size 32bit value 0x12345678 - the first byte sent is 0x12 then 0x34, 0x56, 0x78.

Please visit https://forge.codesys.com/prj/codesys-example/modbus/home to find examples.

InOut:

Scope	Name	Type	Initial	Comment	Inherited from
Input	xEnable	BOOL	FALSE	Enables the server, take over the configuration information fcsSupported and dataModel. If the “data model” (tableDefinitions) contains configuration errors, the Server will not got busy (xBusy = FALSE).	Server
	fcsSupported	SupportedFcs	Constants.SUPPORTED_FCS_SIMPLE_SERVER	Supported “function codes”, accepted at xEnable FALSE => TRUE. In case fcsSupported is not assigned by the application it defaults to |Constants.SUPPORTED_FCS_SIMPLE_SERVER|.	Server
	dataModel	TableDefinitions		“data model”, accepted at xEnable FALSE => TRUE.	Server
	tInactivityInfoTime	UDINT	0	“inactivity info time” (in milliseconds). If no valid requests are received in this time xInactive is signaling inactivity - default = 0 -> no “inactivity info”.	Server
Output	xRunning	BOOL		Server is up and running, waiting for requests.	Server
	xError	BOOL		Error	Server
	eErrorID	Error		Error status	Server
	xInactive	BOOL		No valid requests received for tInactivityTimeOut.	Server
	udiNumMsgRecv	UDINT		Number of request messages received since enabling the Server.	Server
	udiNumMsgReply	UDINT		Number of reply messages send since enabling the Server.	Server
	udiNumMsgExcReply	UDINT		Number of exception reply messages send since enabling the Server.	Server
	udiNumMsgExcReplyIllFct	UDINT		Number of exception reply messages send since enabling the Server, signaling illegal function.	Server
	udiNumMsgExcReplyIllDataAdr	UDINT		Number of exception reply messages send since enabling the Server, signaling illegal data address.	Server
	udiNumMsgExcReplyIllDataValue	UDINT		Number of exception reply messages send since enabling the Server, signaling illegal data value.	Server
	xReadRequest	BOOL		Read request(s) happened since last call, rejected requests included.	Server
	udiNumReadRequests	UDINT		Read request counter, rejected requests included.	Server
	xWriteRequest	BOOL		Write request(s) happened since last call, rejected requests included.	Server
	udiNumWriteRequests	UDINT		Write request counter, rejected requests included.	Server
Input	wsInterfaceName	WSTRING(255)		ETH interface name to bind to, “” to bind to any ETH interface. Only read when rising edge on xEnable occurs.	ServerTCP
	uiPort	UINT	502	ETH port to use. Only read when rising edge on xEnable occurs.	ServerTCP
	xReset	BOOL	FALSE	Reset the server.	ServerTCP
	udiLogOptions	UDINT	LoggingOptions.ServerStartStop	Logging options.	ServerTCP
Output	uiConnectedClients	UINT		Number of actually connected clients.	ServerTCP