“Modbus Slave” Tab

“Modbus Slave” Tab
Parameters	Value	Description
General Settings
Unit-ID	1 … 247	Defines the Modbus unit ID (slave ID)
Behavior on PLC stop	Behavior of the Modbus slave when the controller has halted (controller in “STOP” state)
	Keep last values	Data exchange possible. For Modbus read requests, the last frozen values are returned. For write requests, the values are applied unchanged in the Modbus process image without passing them to the controller.
	No data exchange	No data exchange possible. Modbus requests are always answered by the exception response “ILLEGAL FUNCTION” (0x81).
	Use substitute value	Data exchange possible. For Modbus read requests, substitute values (0) are returned. For write requests, the values are applied unchanged in the local Modbus process image without passing them to the controller.
Behavior on fieldbus error	Behavior of the Modbus slave on detected fieldbus errors (interruption of communication).
	Keep last value	Data exchange is possible. For PLC read functions, the last frozen values from the Modbus process image are returned. For write accesses, the values are applied unchanged in the Modbus process image without passing them to the Modbus master.
	No data exchange	No data exchange is possible.
	Use substitute value	Data exchange is possible. For PLC read functions, the substitute values (0) from the Modbus process image are returned. For write accesses, the values are applied unchanged in the Modbus process image without passing them to the Modbus master.
Response delay [ms]	0 … 32	Transmission of the response to a Modbus request is delayed from the time of processing (read and/or write registry values) by the time set. 32 ms = max. delay 0 ms = no delay The actual time is always greater due to parallel requests/system load. Changes become effective immediately for each subsequent request.
Update Variables	Always Update	Variables are always updated, even if they do not appear in the program, but only used in the Visu Task.
Update Variables	Only when used in the PLC task	Variables are only updated when the appear in the program.
Watchdog settings
Function mode	Advanced mode	The watchdog must be controlled explicitly via commands (see registry 0xFA00 (Watchdog Command)).
Function mode	Simple mode	The watchdog is activated directly with a timeout > 0 s in registry 0xFA01 (Watchdog Timeout). Each trigger restarts both the running as well as the expired watchdog.
Reset timeout [ms]	0 … 65535	Defines the watchdog reset timeout.
Explicit trigger	On	Only writing registry 0xFA00 (Watchdog Command) with the value 0x5555 (WATCHDOG_START) applies as a watchdog trigger (exception: registry 0xFA02 (Watchdog Status)).
Explicit trigger	Off	All valid Modbus requests apply as a watchdog trigger (exception: registry 0xFA02 (Watchdog Status)).
Trigger on state	On	Reading the watchdog status triggers the watchdog.
Trigger on state	Off	Disables watchdog trigger Reading the watchdog status does not apply as a watchdog trigger.
Resetting of the TCP connections	On	Disconnects all Modbus TCP connections when the watchdog expires
Resetting of the TCP connections	Off	Existing Modbus TCP connections remain open.
TCP settings
TCP port	1 … 65535	Port number for the TCP link 1 = min. port number 502 = Modbus default port 65535 = max. port number
Timeout [10 ms]	1 … 65535	Timeout for a TCP link The connection is closed when no more packets are received within the timeout period. Example: Entering “1” results in 10 ms. Entering “600” results in 6 s. Entering “65535” results in 10 min 55 s 350 ms.
Type of Service (IP)
Low Delay	On	Sets the “Low Delay” attribute in the IP header
Low Delay	Off	The “Low Delay” attribute is not set.
High Throughput	On	Sets the “High Throughput” attribute in the IP header
High Throughput	Off	The “High Throughput” attribute is not set.
High Reliability	On	Sets the “High Reliability” attribute in the IP header
High Reliability	Off	The “High Reliability” attribute is not set.
Keepalive (TCP)
Enabled	On	Enables “KeepAlive” for TCP connections
Enabled	Off	Disables “KeepAlive” for TCP connections
KeepAliveTime [s]	0 … 65535	The time span in seconds between the last data packet and the first “KeepAlive” packet (probe)
KeepAliveInterval [s]	0 … 65535	Time between two successive connection attempts if “KeepAlive” packet fails
KeepAliveProbes [Number]	0 … 65535	Number of unanswered attempts until a connection is considered lost
UDP settings
UDP port	1 … 65535	Port number for the UDP link 1 = min. port number 502 = Modbus default port 65535 = max. port number
Type of Service (IP)
Low Delay	On	Sets the “Low Delay” attribute in the IP header
Low Delay	Off	The “Low Delay” attribute is not set.
High Throughput	On	Sets the “High Throughput” attribute in the IP header
High Throughput	Off	The “High Throughput” attribute is not set.
High Reliability	On	Sets the “High Reliability” attribute in the IP header
High Reliability	Off	The “High Reliability” attribute is not set.
Multicast settings
Multicast group 1 … 5	xxx.xxx.xxx. xxx	Defines the IP address of multicast groups 1 to 5
RTU settings
Parameter takeover from master		RTU settings of the master are applied.
		RTU settings for master and slave are not synchronized.
	This option is only displayed for the Modbus slave.
Device file	/dev/tty RUNTIME0	Description of the serial interface for the target system The file is only displayed for the Modbus master.
Interface configuration	RS232 RS485	Defines the interface type used
Baud rate [Bd]	50 … 921600	Sets the communication baud rate
Serial mode	RTU	Display of the Modbus transfer mode (coding/packet structure) The mode is only displayed for the Modbus master.
Daten bits	8	Generally sets the data bits for RTU to 8 bits
Parity	Defines the parity for the parity check
	Even	Even parity
	Odd	Odd parity
	None	No parity check 2 stop bits must be selected in the configuration for this setting.
Stop bits	1	1 stop bit in the frame Must be used when even or odd parity has been selected.
Stop bits	2	2 stop bits in the frame Must be used when no parity is selected.
Flow control	Data flow control Supported only for the setting “RS-232” for the physical interface
	None	No data flow control
	RTS/CTS	Hardware flow control
InterFrameTimeout [ns]	0 … 4294697295	Defines the time required between two frames so that they are recognized as separate frames (0 = default value of the Modbus RTU specification)
InterCharacterTimeout[ns]	0 … 4294697295	Defines the maximum time between two characters within a frame so that it is recognized as a valid frame (0 = default value of the Modbus RTU specification)
Timeout in [ms]	1 … 65535	If the request is not processed in the Modbus slave within the specified time, there is no response to the request. This setting is only displayed for the Modbus slave.
Request interval [ms]		Time in ms between two successive requests This setting is only displayed for the Modbus master.
Response timeout [ms]		Wait time in ms until a request is repeated