Configuring the MES1A/B
•If any Modbus TCP masters on your system use 0 for all Unit ID fields, select a slave address that matches the Modbus/RTU slave attached to your MES1A/B. You will not be able to connect multiple slaves to the
Allow Modbus Broadcasts
If you configured the Slave Address for any number between 1 and 255 the
Allow Modbus Broadcasts does not appear in the menu.
When a Modbus/RTU slave receives a slave address of 0 it interprets this as a broadcast message. All slaves accept the message. Setting the Allow Modbus Broadcasts (1=Yes, 2=No)to No reassigns a Unit ID of 0 from a Modbus TCP master as a slave address 1. This ensures that a Unit ID is not interpreted as a broadcast message.
Use MB/TCP 00BH/00AH Exception Responses
In Modbus/RTU, when a master initiates a query it expects to receive a response. If it does not receive one within an acceptable length of time it interprets the silence as an indication that a communications error has occurred. Because delays in TCP/IP networks are not predictable, problems can occur. To address this, Modbus/TCP defines two exception codes that can be enabled to be sent in the event of a communications failure.
1 = No
If Use MB/TCP 00BH/00AH Exception Responses (1=No 2=Yes)is disabled (1=No), the MES1A/B operates like a Modbus/RTU slave. It answers timeouts,
2 = Yes
If the Use MB/TCP 00BH/00AH Exception Responses (1=No
2=Yes)is enabled (2 = Yes), the MES1A/B will return the following codes under any of the conditions described:
0A (hex) - Path Unavailable
•If it receives a query from a Modbus master in which the Unit ID specifies a Slave Address not listed in the Unit ID to IP Mapping Table
•If the TCP socket fails to open.
Manual Documentation Number: |
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