Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 120)

Diagnostics Methods
Chapter 7
7-8
A communication retry is a re-transmission of data that occurs when the
original transmission is unsuccessful. If the I/O adapter does not respond
or sends invalid data when the scanner communicates to the I/O adapter,
the scanner executes a retry.
You can track the retry count by monitoring status file 3 (see Figure 7.5).
Figure 7.5
I/O Communication Retry Counts (Status File 3)
17
Adapter # Starting
I/O group
0 0
2
4
6
1 0
2
4
6
16 15 14 13 12 11 10 07 06 05 04 03 02 01 00
word 0
word 1
word 2
word 3
word 4
word 5
word 6
word 7
word n
.
.
.
To find the word that stores the retry count for an I/O adapter:
Adapter # in decimal x 4 = the first of the words that stores the retry
counts for the adapter. The particular
word depends on the starting I/O group.
For example, the retry counts for adapter 10 are in words 40 to 43 (S3:40 to S3:43) 15181
Important: The processor does not create status file 3 at power-up. You
must create it in memory by using the create command.
If the retry count is high for an I/O channel, check to see if it is caused by
one of the following:
loose connection with the twinaxial cable (cat. no. 1770-CD) that
connects from the scanner’s terminal arm to the I/O adapter
noise problem with the twinaxial cable (cat. no. 1770-CD) that connects
from the scanner’s terminal arm to the I/O adapter
improper installation of I/O terminator resistors along the I/O channel
Refer to the PLC-3 Family Controller Installation and Operation Manual
(publication 1775-6.7.1) for detailed information.
I/O Communication Retry
Counts (Status File 3)