Rockwell Automation 1785 PLC-5 User Manual download pdf (Page 143)

Publication 1785-UM012D-EN-P - July 2005

Communicating with Devices on a DH+ Link 9-11

Monitoring General Status

Status Field Word(s) Description

SDA or SDN transmit retry 28 Total number of SDA or SDN messages that were re-transmitted. Some reasons why the station

would retry a message are:

the ACK was lost or corrupted on an SDA message, indicating a possible noise problem

the original message was NACKed

Duplicate node 17 Number of times the station has detected the same station address as itself on the network. As

a result, the station goes offline.

Claims lost 11 Number of times the station did not win the claim token sequence. See claims won below for

more information.

Network dead 9 Number of times the station detects no traffic on the network.

This usually occurs when the station with the token is powered down or is removed from the

network. The other stations are waiting for the token to be passed to them. Eventually a network

dead situation is declared and a claim token sequence initiated. (See claims won for more

information.)

Claims won 10 Number of times the station has won the claim token sequence.

All the stations initiated a claim token sequence when a network goes down, is just powered up

and the stations on the network detect that no one has the token, or when a station with the

token is powered down or removed from the network. A claim token sequence is when all the

stations on a network attempt to claim the token. When multiple stations attempt to claim the

token, the lowest numbered station wins.

Dropped token 18 Number of times that the station detected that a duplicate node existed on the link and

consequently dropped itself off the link

A station determines that there is a duplicate node when it detects that the response to a

message or solicit successor is incorrect. For example, if a response is received from a station

which was not communicated with, then the sending station assumes that the response is for a

packet sent by another station with the same node number. Once the station drops itself off the

link, it waits indefinitely to be solicited back into the network. It will only be solicited back into

the network if the duplicate node is removed from the link, because station numbers that already

exist on the link are not solicited into the network.

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Rockwell Automation 1785 PLC-5 User Manual Page 143