Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 125)

Diagnostics Methods
Chapter 7
7-13
Diagnostic Loop Command
You can use this command to check the integrity of transmissions over the
communication link. The command message transmits up to 243 bytes of
data to a remote station. The receiving station should reply to this
command by transmitting the same data back to the scanner.
For example:
Command block in data table:
0012 0006 0000 0000 0102 0304 0506 0708 090A 0B0C 0D00
Response block in data table:
0000 0011 4600 0200 0102 0304 0506 0708 090A 0B0C 0D00
Diagnostic Status Command
You can use this command to read a block of status information from the
remote station. The reply to this command contains the diagnostic status
information in the response data. Each remote station defines the data sent
back in response. The scanner sends back 18 bytes as defined in
Table 7.H.
For example:
Command block in data table:
0005 0006 0000 0003
Response block in data table:
0000 0016 4600 0300 0246 1003 5088 5E00 4002 0000 111B
0400 0000
Diagnostic Read Command
You can use this command to read the remote stations diagnostic counters.
Use the diagnostic status command to obtain the starting address of the
diagnostic counters.
The first two bytes of the command data is the address of the counters (low
byte/high byte) as returned from a diagnostic status command. The third
byte is the number of bytes to be returned; 18 bytes for the scanner.
The response data contains the diagnostic counters. The scanner DH
counters are defined in Table 7.F and DH+ counters in Table 7.G.
Command block in data table:
0008 0006 0000 0001 5E00 1200
Response block in data table:
0000 0016 4600 1700 7E4B 7F4B 0000 0000 0000 0000 0000
0000 0000