Rockwell Automation 1770-KF2 Data Highway or Highway Plus Interface Module User Manual User Manual
Page 182
Error Reporting
Chapter 7
7Ć27
0.
Bad CRC or I/O error on ACK. Same causes as bad CRC on
messages.
1.
ACK Timeout: Counts the number of times that the sender timed
out waiting for an acknowledgment. This is a common error and will
be one of the first to respond to reflections or low-level noise on the
highway. It seems to be especially sensitive to problems on longer
cables. It will also appear often if the receiver or transmitter
circuitry on a module is marginal or if the cable connections are
loose.
2.
Contention: Counts the number of times contention was detected.
This will also appear quickly on noisy or overlength cables. This
counter corresponds to Error 93.
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. Currently the only other implemented ACK code is
buffer overflow. This condition should never occur except possibly
when debugging new computer programs.
4.
Returned Messages: Counts the number of times the highway
driver returns a message to sender. Each count corresponds to one
local error bit set or one reply message lost.
5.
Transmit/Memory Full: Counts the number of times the highway
driver returns a message to sender. Each time this happens the
message is placed in a waiting queue for a half second. Each
message will be retried five times 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