Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 156)

9–18 Diagnostic Counters
Publication 1770Ć6.5.16 - October 1996
This counter byte Counts the number of
15
Duplicate frames received.
A duplicate frame is sent by a transmitter when it fails to receive an
ACK. If the reason it failed to receive an ACK was that the ACK was
lostĊrather than that the original message was lostĊthe duplicate
is redundant and is discarded. Any two successive messages
between polls that have the same sequence number fields and the
same command or reply bits are assumed to be duplicates.
16 Aborts received.
The HDLC abort signal is not used on a DH link but can be detected
by the serial input or output, in certain circumstances. Some nodes
whose addresses match the ringing pattern after a transmitter
shutoff, can be particularly susceptible to this error (nodes 36, 76,
and 176, for example). These numbers depend on link
configurations.
17, 18 Messages successfully transmitted.
19, 20 Messages successfully received.
21, 22 ACKs received.
23, 24 ACKs sent.
25, 26 NACKs received.
27, 28 NACKs sent.
29 Replies that were lost because they could not be delivered over the
link.
Undeliverable commands can be signalled to the user, because the
user" is located in PC memory, and can always be reached.
If a reply message cannot be delivered over the link, there is no way
to signal the user (of that message)Ċwho is also on the linkĊthat
this node cannot signal a reply. The local user is not concerned with
the problems of the remote user and can take no meaningful action,
so there is not much to do but destroy the message and count it.
30 Timeouts preset.
31 Values set by diagnostic commands or set by default on powerĆup.
32 ENQs preset.