Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Instrukcja Użytkownika Pobierz pdf (Strona 146)

9–8 Diagnostic Counters

Publication

17706.5.16 - October 1996

Cat. Nos. Link Pages

1770 KF2

DH 9-8

1770KF2

DH+

9-11

1770KF3 DH485 9-3

1770KFC DF1 9-13

1770KF2 and 1771KE/KF DH and Asynchronous Link

Diagnostic Counters

This counter byte Counts the number of

Bad CRCs or I/O errors on ACK.

Same causes as bad CRC on messages.

Times the sender timed out waiting for an acknowledgment.

This is a common error and is the first to respond to reflections or

low level noise on the link. It is sensitive to problems on longer

cables. It also appears if the receiver or transmitter circuitry on a

module is marginal or if the cable connections are loose.

Times contention was detected.

This counter corresponds to error 93. This also appears quickly on

noisy or overlength cables.

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

status code other than memory full.

Currently the only other implemented ACK code is buffer overflow.

This condition should never occur except when debugging new

computer programs.

Times the link driver returns a message to sender.

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

message lost.

Times the link driver returns a message to sender.

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

for 0.5s. Each message is retried five times before it is returned to

the sender.

Times this node grabbed mastership of the link 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.

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

that was expected to takeover failed to respond.

This happens often 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. This usually leads to the second node

detecting contention and relinquishing.

Times that the receiver received a status frame instead of a

message frame.

This counter is never incremented because the message size is

checked first, and all status messages are too small to be accepted.

1770 Cat. Nos.

1 2 ... 141 142 143 144 145 146 147 148 149 150 151 ... 250 251

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