Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manual de usuario descargar pdf (Pagina 154)

9–16 Diagnostic Counters

Publication

17706.5.16 - October 1996

This counter byte Counts the number of

30 Replies lost because they could not be delivered over the DH link.

Undeliverable commands can be signaled to the user, because the

user" is located in PC memory, and can always be reached.

If a reply message cannot be delivered over the link, there is no way

to signal the user (of that message)who is also over the

highwaythat this node cannot signal a reply. The local user is not

concerned with the problems of the remote user and can take no

meaningful action, so there is not much to do but destroy the

message and count it.

Important: An intelligent device can read the memory of the

1771-KC it is connected to by setting the destination

equal to the module address.

1771KC DH Diagnostic Counters

This counter byte Counts the number of

0 Bad CRCs on ACK.

1 Times the sender timed out waiting for an acknowledgement.

This is a common error and is one of the first to respond to

reflections or lowlevel noise on the link. It seems to be especially

sensitive to problems with longer cables. It also shows up if the

cable connection are loose.

2 Times contention was detected.

This also shows up quickly on noisy or cables that are too long.

This counter corresponds to error 93.

3 Times the ACK was successfully received but contained a nonzero

status code other than memory full.

4 Times the highway driver returns a message to sender with a

nonzero status code because a reply was not received from a

remote node.

Each count corresponds to one local error bit set or one reply

message lost.

5 Times the receiving node's memory was full.

Each time this happens, the message is placed on a waiting queue

for 0.5s. Each message is retried five times for memory overflow

before it is returned to sender.

6 Times this node grabbed mastership of the highway because it

timed out while waiting to hear a valid frame.

On a DH link that has just been powered up, there should be only

one node that has this counter incremented.

7 Times that this node has tried to relinquish mastership and the node

that was expected to take over failed to respond.

This happens on a noisy link because the noise is mistaken for a

poll response, and the wrong node is selected as the next master.

When this occurs, the old master resumes polling. It also can

happen on a long link, if the poll response is very attenuated and is

not picked up by the carrier detect circuit. If the new node does

respond but the old master does not hear it, the old master records

a false poll and continues polling, and the new master starts polling

also. This usually leads to the second node detecting contention

and relinquishing.

1 2 ... 149 150 151 152 153 154 155 156 157 158 159 ... 250 251

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Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manual de usuario Pagina 154

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