Rockwell Automation 1771-KA2 Communication Adapter Module - Manual (Page 70)

Status Words
Chapter 6
6-6
The upper byte of the ERROR CODE storage word (bits 10-17) stores a
2-digit BCD value. This value gives supplemental error or fault
information, depending on the type of ERROR CODE displayed. It may
have one of two meanings:
Reference number
Counter
For ERROR CODES 01-29, the upper byte stores a 2-digit reference
number. This number points to the location of a programming error
within the communication zone of program. This error may be an
incorrect instruction or an improper address entered within a rung of the
communication zone. In this numbering scheme, the header rung of the
communication zone of program is designated as “00.” Subsequent
communication zone rungs are numbered sequentially.
Note that ERROR CODES 01-29 are intended as aids in start-up
debugging of the communication zone of program. Thus, the reference
number stored in this word can be a valuable tool for debugging purposes.
For ERROR CODES 30-99, the upper byte stores a 2-digit counter. This
counter shows the number of ERROR CODES 30-99 written into the
storage word by the communication adapter module. The counter
increments each time a different ERROR CODE storage word.
These codes are generally to be displayed on a programming terminal
rather than used in application programming. They have special value in
station start-up, when programming errors are detected in the
communication zone of program.
By viewing the header rung of the communication zone, the programmer
can examine a displayed ERROR CODE and the least significant digit of
the counter in this word. (Section titled “Header Rung,” chapter 5,
describes a header rung.)
In some instances, however, it may be preferable to display the 2-digit
error code using a 7-segment BCD numerical display controlled from
output modules of the controller. This 7-segment display, mounted at an
operator’s station, can provide a useful troubleshooting aid for quickly
locating fault conditions.