Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 127)

Diagnostics Methods
Chapter 7
7-15
Table 7.G
DH+ Diagnostic Counters
Byte: This counter increments when the scanner:
1 & 2 successfully sent a message
3 & 4 successfully received a message
5 can not deliver a message due to a NAK or after using up maximum
retries
6 did not receive a response before the response timeout value was
reached
7 received a NAK
8 must send a message retry as a result of CRC error, illegal length, not
its destination, the source was not the expected station, or a timeout
9 sent a NAK because there was no memory available
10 sent a NAK because of the received message contained an undefined
LSAP
11 receives a message which was received previously
12 has to send a token pass retry
13 receives an aborted packet
14 receives a packet that had a CRC error
15 receives an illegal size packet which was either less than 3 bytes or
larger than 271 bytes
16 detects a duplicate token on the link
17 recovers from a duplicate node condition
18 detects a link dead timeout