User guide

Communication Capabiliites
86
890 USE 108 00 August 2001
Modbus Plus LEDs
Flash Pattern
Details
The MB Plus LED is a green indicator that shows the type of communications activity
on the Modbus Plus port on A984-145, E984-245/255/265/275/285 Controllers. A
specific flash pattern indicates the nature of the Modbus Plus communication
activity:
The following table lists the LEDs flash patterns and their meanings.
LED Flash Patters 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 after just being powered up, or after hearing a
message from another node with the same 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 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.
Three flashes, then OFF
for 1.7 seconds
The node is not hearing any other nodes. It is periodically
claiming the token, but finding 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 has heard a valid message from another node that is
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 then
changes to the pattern of one flash every second.
On steady The address switch setting is set to an invalid Modbus Plus
address (i.e.: 0 or > 64).