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CHAPTER 4: WEB GRAPHICAL USER INTERFACE (GUI)
4.2.11 MODBUS
MODBUS RTU is a non-proprietary serial communications protocol that is widely used in the process control industry
actuation. The AlertWerks Gateway can represent both "master" and "slave" devices and supports both Modbus RTU
(RS-485) and Modbus TCP protocols.
The hub currently only supports Modbus with an RJ-45 connector (RTU and TCP) on its expansion port. For just
Modbus, only pins 1 and 2 are used (Modbus A/+ and Modbus B/-). You cannot use other sensor ports for Modbus other
than the expansion port.
IMPORTANT: When you use Modbus, you can't connect expansion boards to the unit!
Standard can only use the Modbus Virtual Sensors.
NOTE: Modbus queries are slow (up to 3 seconds). This is per Modbus protocol definition, it's not an AlertWerks
Gateway limitation.
The more sensors you have, the bigger the polling interval must be.
FIGURE 4-36. SITE NOT SECURE SCREEN
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