Rockwell Automation 2708-DH5B2L_DH5B4L Attended Workstation - Manual (Page 78)

Chapter 8
Host Communications
8–3
The middle pair of numbers in the status records, the retry count, may be
used to diagnose improper cabling, or to identify workstations which may be
malfunctioning. Normally all retry counts should be 00.
If the retry count has a non-zero value, then the record following that prefix
had to be sent more than once in order for it to reach the Master. If certain
workstations require retries on a frequent basis, then it is recommended that
the cabling be checked for these workstations. If one workstation only is
registering consistent retries, consider swapping it with another workstation
to show if it is cabling or the workstation which is the cause of the problem.
If the number of retries shown in prefix becomes much greater as the
workstations creating those records are farther from the Master along the
network cable, then a faulty or poorly grounded cable is suspect. See the
Chapter 2 for information pertaining to cabling, termination and network
layouts.
The network directives are a set of commands which can be sent from the
Host to any workstation on the network. All responses are directed to the
Host, and take the form:
<10-byte prefix> ND <command letter> data
where:
10-byte prefix is the prefix attached to all records (as described
above)
ND appears in positions 11 and 12, and indicates a
Network Diagnostic
<command letter> is a single UPPER case character which identifies
the data which follows
data the useful portion of the response.
For example, the response to the <T directive (a request for time) might be:
0808001400ND T 1743077788020506
Using Retry Counts
for Network Diagnosis
Responses to
Network Directives