Chapter 3: Modicon PLCs Using Modibus Plus
31
Cabling Diagrams
Communications between the Operator Station and Modbus Plus follows the Modicon standard. See
the PanelMate Power Series Modbus Plus Interface Instructions IL (01-50463) for additional
information. The Operator Station should be wired like a node on the Modbus Plus Network. The
Modicon Part number for the connector required is: AS-MBKT-085 (if the Operator Station is at an
inline node) or AS-MBKT-185 (if the Operator Station is at an extreme end of the network).
The figures below shows a single and dual cabled Modbus Plus interface board.
Note:
The Dual Channel Modbus Plus interface board is no longer available.
Single Cable Interface Board
Dual Cable Interface Board
LEDs
The green LED is used to help determine the current status of the Modbus Plus interface board. The
following is a list of possible indications:
Note:
The two red LEDs, labeled A and B, on the dual cabled Modbus Plus interface board indicate
communication errors in either the Modbus Plus A port or the Modbus Plus B port. If an
error occurs, the corresponding red error LED will turn on while the communication error
exists.
Network Communication Status
Modbus Plus status is shown by flashing a repetitive pattern on the green indicator. The patterns are:
Six flashes per second
The Modbus Plus interface board’s normal operating state. The indicator flashes each time the
board transmits at its Modbus Plus port. All nodes on the network should be flashing this pattern.
If a port indicator is OFF continuously, the board is not transmitting at its port.
One flash per second
The Operator Station node is offline after just being powered up, or after hearing a message from
another node with the same network address (duplicate addresses are not allowed). In this state,
the node monitors the network and builds a table of active nodes and token-holding nodes. It
remains in this state for five seconds, then attempts to go to its normal operating state.
Two flashes, then OFF for two seconds
The Operator Station node is hearing the token being passed among other nodes, but is never
receiving the token. Check the network link for an open or short circuit or defective termination.
