Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 146)

9–8 Diagnostic Counters
Publication 1770Ć6.5.16 - October 1996
Cat. Nos. Link Pages
1770 KF2
DH 9-8
1770ĆKF2
DH+ 9-11
1770ĆKF3 DH485 9-3
1770ĆKFC DF1 9-13
1770ĆKF2 and 1771ĆKE/KF DH and Asynchronous Link
Diagnostic Counters
This counter byte Counts the number of
0
Bad CRCs or I/O errors on ACK.
Same causes as bad CRC on messages.
1
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.
2
Times contention was detected.
This counter corresponds to error 93. This also appears quickly on
noisy or overĆlength cables.
3
Times the ACK was successfully received but contained a nonĆzero
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.
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 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 reĆtried five times before it is returned to
the sender.
6
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.
7
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.
8
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.