Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 152)

9–14 Diagnostic Counters
Publication 1770Ć6.5.16 - October 1996
Cat. Nos. Link Pages
1771ĆKA, 1771ĆKA2, and 1774ĆKA DH 9-14 , 9-15
1771ĆKC DH 9-16 , 9-18
1771ĆKE/KF DH 9-8
1771ĆKG, ĆKGM DH 9-19
1771ĆKA, 1771ĆKA2, and 1774ĆKA DH Diagnostic Counters
This counter byte Counts the number of
0
Times CRC was in error on an ACK.
1 Times the sender timed out waiting for an acknowledgement.
Common error that occurs with error reflections or noise on the link
(sensitive to problems on longer cables). It also shows up if the
receiver or transmitter circuitry on a module is marginal, or if cable
connections are loose.
2 Times contention was detected.
This appears quickly on noisy or long cables. This counter
corresponds to error 93. If 93 is a common error on your link,
expect 37 (start bit timeout) errors also, since any reply that
experiences contention is not reĆtried.
3 Times the ACK was successfully received but contained a nonĆzero
status code other than memory full.
Only other implemented ACK code is buffer overflow. This condition
should never occur except when debugging new code.
4 Times the link driver returns a message to sender.
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 reĆtried five times for memory overflow
before it is returned to sender.
6 Times this node grabbed mastership of the DH link because it timed
out while waiting to hear a valid frame.
On a link that has just been powered up, there should be only one
node that has this counter incremented.
7 Times this node has tried to relinquish mastership and the node that
was expected to take over failed to respond.
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.
Also happens 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
responds, but the old master does not hear it, the old master
records a false poll and continues polling. The new master starts
polling also. This usually leads to the second node detecting
contention and relinquishing.
8 Times the receiver received a status frame instead of a message
frame.
This occurs only if a poll timeout is imminent (a master has had
mastership for more than 170ms) and the node has disabled its
address recognizer to test for any valid traffic.
1771 Cat. Nos.