Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual User Manual
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Error Reporting
Chapter 7
7Ć24
3.
Bad ACK Status: Counts the number of times the ACK was
successfully received but contained a non-zero status code other than
memory full.
4.
Returned Messages: Counts the number of times the highway
driver returns a message to sender with a non-zero status code
because a reply was not received from a remote station. Each count
corresponds to one local error bit set or one reply message lost.
5.
Transmit/Memory Full: Counts the number of times that the
receiving station’s memory was full. Each time this happens the
message is placed in a waiting queue for a half second. Each
message will be retried five times for memory overflow before it is
returned to sender.
6.
Poll Timeout: Counts the number of times this station grabbed
mastership of the highway because it timed out while waiting to hear
a valid frame. On a highway that has just been powered up there
should be only one station that has this counter incremented.
7.
False Poll: Counts the number of times that this station has tried to
relinquish mastership and the station that was expected to take over
failed to respond. This happens often on a noisy highway because
the noise is mistaken for a poll response, and the wrong station is
selected as the next master. When this occurs, the old master
resumes polling. It also can happen on a long highway if the poll
response is very attenuated and is not picked up by the carrier detect
circuit. If the new station does respond but the old master does not
hear it, the old master will record a false poll and continue polling;
and the new master will start polling also. This usually leads to the
second station detecting contention and relinquishing.
8.
Receiver Heard Status: Counts the number of times that the
receiver received a status frame instead of a message frame. This
should occur only if a poll timeout is imminent (a master has had
mastership for more than 170 ms) and the station has disabled its
address recognizer to test for any valid traffic. The probability of
errors in #8, 9, and 10 increases substantially.
9.
Frame Too Small: Counts the number of frames that were rejected
because the header was incomplete. This should only be counted
because of undebugged software or in the unlikely event that a bad
frame fooled the CRC checker.