3.2.41        Send Where I Am to IP Address

Defines the IP Address (for example to send a Where I am message.  This allows Dynamic IP address to be used by a SCADA node if it is configured as a WASCADA device to another SCADA node.  For more information about WASCADA see 14.6 SCADA Node from another Project.

Dynamic IP Addresses for polled devices.

Now WebAccess can poll devices, including WebAccess SCADA nodes, with dynamic IP address. As long as the devices can send "Where I am" message according to the following format. WebAccess SCADA node will search the device name in the message against the device name in WebAccess device configuration, if the names match, WebAccess use the new IP from the message to poll the device. In order to support this feature, a user needs to configure WebAccess SCADA node Modbus listening port to take "Where I am" message. This Modbus listening port is the same port if the SCADA node also servers as a device polled by another SCADA node. For WebAccess with dynamic IP acting as a device to be polled by another SCADA node,  a user needs to configure the IP, port and frequency to send "Where I Am" Message. If NAT or port mapping is used in the router, user needs to set it correctly to make this feature works.

The device sends its ID using Modbus TCP format, with command code 0x7E.

The format is defined as :


Byte 0 : Transaction Identifier H

Byte 1 : Transaction Identifier L

Byte 2 :  Modbus protocol identifier, should be 0

Byte 3 :  Modbus protocol identifier, should be 0

Byte 4 :  Data Length H, 0

Byte 5 :  Data Length L, 64

Byte 6 :  Unit Address, 0

Byte 7 : Command code 0x7E

Byte 8-39 : Device Name

Byte 40-69 : reserved