Dev_Tasks
To program communications over the Ethernet network using Modbus/TCP Channel commands use Communications Request (COMMREQ) Modbus/TCP Channel commands.
Reference: TCP/IP Ethernet Communications for the Series 90 PLC User's Manual  GFK-1541B.
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Ethernet_Module_Task_Id
0 for all ModbusTCP Ethernet interface
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Wait_Flag	
This flag determines whether PLC will wait until the device serial ports receive the intended data before continuing. The request can either send a message and wait for a reply, or send a message and continue without waiting for a reply. If the Command Block specifies that the program will not wait for a reply, the Command Block contents are sent to the device and ladder program execution resumes immediately. This is referred to as NOWAIT mode. If the Command Block specifies that the program will wait for a reply, the Command Block contents are sent to the targeted device and the CPU waits for a reply for a maximum length of time specified in the Command Block. If the device does not respond in that time, ladder program execution resumes. This is referred to as WAIT mode.
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Idle_Tmout	
The idle timeout value is the maximum time the PLC waits for the device to acknowledge receipt of the request. For NOWAIT, this value is not used. (Any timeout value is ignored; it can be zero.) If WAIT is selected, this word specifies the idle timeout period, in 100-microsecond increments.
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Max_Comm_Tm	
This word contains the maximum amount of time the program should hold the window open when the device is busy. For NOWAIT, this value is not used. (Any timeout value is ignored; it can be zero.) If WAIT is selected, this word specifies the maximum time in 100 microsecond increments.
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Open ModbusTCP Connection
The Open Modbus/TCP COMMREQ requests the communication subsystem to associate a channel with a remote Modbus/TCP device. Using which PLC may transfer data to and from a remote device. Once a channel is allocated for Modbus/TCP Client communications, the channel remains allocated. The channel connection is released only when: the application program closes the channel, the channel is automatically closed because the PLC transitions to STOP, or the underlying TCP connection is terminated.
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Close ModbusTCP Connection
Close ModbusTCP Connection closes a Modbus/TCP Client Connection by issuing the Close Modbus/TCP Client Connection COMMREQ. The Close COMMREQ closes the underlying connection and frees the channel for other communication tasks. An error response is returned if the channel number in the COMMREQ identifies a non-
Modbus/TCP Client connection or an inactive channel.
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Read Data Mem ModbusTCP
The Read Data from a Modbus/TCP Device COMMREQ requests a data transfer from a Modbus/TCP device to the PLC. The Read Data COMMREQ must reference an active Modbus/TCP channel previously established with the Open Modbus/TCP Client Connection COMMREQ. Registers or Coils may be read from the remote Modbus/TCP device.
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Read Exception Status ModbusTCP
The Read Exception Status data from a Modbus/TCP Device COMMREQ requests a data transfer from a Modbus/TCP device to the PLC. This COMMREQ must reference an active Modbus/TCP channel previously established with the Open Modbus/TCP Client Connection COMMREQ.
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Write Data ModbusTCP
The Write Data to a Modbus/TCP Device COMMREQ requests a data transfer from the PLC to a Modbus/TCP server. The Write Data COMMREQ must reference an active Modbus/TCP channel previously established with the Open Modbus/TCP Client Connection COMMREQ. Registers or Coils may be written to the remote Modbus/TCP device. A PLC data area is the source for the data written to the Modbus/TCP device. The source of data can be any of the PLC data areas.
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Channel_Number
Channel Number specifies the channel number to be used by Commreq for the Modbus/TCP Client connection. Channels 1-16 are valid for Client communications.
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Address_Type
Address Type specifies the type of IP Address specified for the remote device. A value of one (1) is required in this word.
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Length_of_IP_Address
Length of IP Address specifies the length of the IP Address. A value of four (4) is required in this word.
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IP_Address
IP Address 1 specifies the value of the first octet of the IP Address.
Below are the global and other specialized IPv4 address blocks that have been assigned by the Internet Assigned Numbers Authority (IANA).  It does not address IPv4 address space assigned to operators and users through the Regional Internet Registries.  It also does not address allocations or assignments of IPv6 addresses or autonomous system numbers.
   Address Block             	Present Use
*************************************************************************************************
0.0.0.0            		'This' Network (Not a valid IP address). This refers to source hosts on 'this' network
10.0.0.0			Private-Use Networks
4.0.0.0           		Public-Data Networks
24.0.0.0           		Cable Television Networks
39.0.0.0			Reserved but subject to allocation
127.0.0.0          		Loopback
128.0.0.0         		Reserved but subject to allocation
169.254.0.0	       	Link Local
172.16.0.0        		Private-Use Networks
191.255.0.0		Reserved but subject to allocation
192.0.0.0         		Reserved but subject to allocation
192.0.2.0         		Test-Net
192.88.99.0	       	6to4 Relay Anycast
192.168.0.0	       	Private-Use Networks
198.18.0.0		Network Interconnect Device Benchmark Testing
223.255.255.0		Reserved but subject to allocation
224.0.0.0          		Multicast
240.0.0.0			Reserved for Future Use
*************************************************************************************************
AVOID THESE ADRESSES.
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Modbus_Function_Code
Registers or Coils data may be read from the remote Modbus/TCP device. The Modbus Function Code specifies the data type.
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Modbus_Fx_Code_Exc_Stat
Exception status data may be read from the remote Modbus/TCP device. The Modbus Function Code specifies the data type.
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Local_PLC_Memory_Type
Local PLC Memory Type: This Words and next specify the location in the local PLC where the Ethernet Interface will store data received from the remote device 
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Local_PLC_Starting_Address
Local PLC Memory Address determines the starting address in the local PLC in which the data from the remote device is to be stored. The value entered is the offset (1- based) from the beginning of PLC memory for the memory type and mode specified in previous Word. This offset will be either in bits, bytes, or words depending on the mode specified. Valid ranges of values depend on the PLCs memory ranges. The user is responsible for assuring that this area is large enough to contain the requested data without overwriting other application data.
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Address_In_Remote_Server
Remote Device Address specifies the address in the remote Modbus/TCP device. Note: The function code determines the Modbus address area 3xxxx or 4xxxx, This word is the address within this area (e.g. you enter 200 not 30200 for accessing 30200). For Read, local PLC will read this address for write local PLC will write at this address.
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Address_In_Remote_Server_C
For "Read Exception Status ModbusTCP", Address In Remote Server is always 0.
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NoOfRegs_in_RmtDevice_C
For "Read Exception Status ModbusTCP", No Of Registers in Remote Device is always 1.
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No_Of_Registers_in_Rmt_Device
Number Registers in Remote Device specifies the quantity of registers (16bit words) to read/write from the remote device.
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Unit_Identifier
Unit Identifier is the Modbus/TCP Unit Identifier, a special control code used in a Modbus/TCP message. The default is 1.This value is 1 for most Modbus/TCP devices except if an Ethernet to Serial bridge is used to multidrop to Modbus RTU devices.
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Modbus_Function_WriteCode
Registers or Coils may be written to the remote Modbus/TCP device. The Modbus Function Code specifies the data type. Function Code 5, Force Single Coil, is the only coil operation supported by the Modbus/TCP Client. This function forces a Coil On or Off. To force a coil off, the value zero (0) is used as COMMREQ data value. To force a coil on, the value one (1) is used as the COMMREQ data value.
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