User guide

Troubleshooting and Maintenance
216
890 USE 108 00 August 2001
Modbus Plus
LEDs A984-145,
E984-245/255/
265/275/285
The MB Plus LED is a green indicator that shows the type of communication activity
on the Modbus Plus port of the controller. A specific flash pattern indicates the
nature of the current Modbus Plus communication activity:
The following table explains the flash patterns for the Modbus Plus LEDs.
LED Flash Pattern Description
Six flashes per
second
The normal operating state for a Modbus Plus node. The node is
successfully receiving and passing the token. All nodes on the network
should be flashing this pattern.
One flash per
second
The node is offline immediately after power up, or after hearing a
message from a node with the same address. (Duplicate addressing is
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 it attempts to go to its normal operating state.
Two flashes, then
OFF for two
seconds
The node is hearing the token being passed among other nodes, but it
never receives the token. Check the network link for an open or short
circuit, or for a defective termination.
Three flashes, then
OFF for 1.7 seconds
The node is not hearing other nodes. It periodically claims the token,
but it finds no other node to which to pass it. Check the network link for
an open or short circuit, or for a defective termination.
Four flashes, then
OFF for 1.4 seconds
The node heard a valid message from another node, using the same
address as this node. The node remains offline in this state as long as
it continues to hear the duplicate address. If the duplicate address is
not heard for five seconds, the node changes to the pattern of one flash
every second.