Details
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Type:
Change
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Status: Closed
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Priority:
Minor
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Resolution: Fixed
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Affects Version/s: None
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Component/s: None
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Labels:None
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Sprint:VARNA KW36 / 37, VARNA KW38 / 39, VARNA KW42 / 43
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Account:SPC Open Modbus TCP (SPCOPENMODTCP)
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Epic Link:
Description
To fulfill the requirement of the specification MODBUS Messaging on TCP/IP Implementation Guide V1.0b Modbus-IDA (October 24, 2006) there should be no limit in the usable Unit identifier
Excerpt from the specification:
When addressing a MODBUS server connected directly to a TCP/IP network, it’s recommended not using a significant MODBUS slave address in the “Unit Identifier” field. In the event of a re-allocation of the IP addresses within an automated system and if a IP address previously assigned to a MODBUS server is then assigned to a gateway, using a significant slave address may cause trouble because of a bad routing by the gateway. Using a non-significant slave address, the gateway will simply discard the MODBUS PDU with no trouble. 0xFF is recommended for the “Unit Identifier" as non-significant value.
Remark : The value 0 is also accepted to communicate directly to a MODBUS/TCP device.