Indirect addressing error analysis - Database & Sql Blog Articles

If the last instruction in the program does not have a comment symbol "//" in front of it, the program will fail to switch to the running mode after downloading, and the SF light will be activated.

The last instruction is commented out (this instruction is not executed). When the error occurs, the diagnostic buffer of the CPU module contains the following information:

Event 8 / 15: Event ID 16# 2523

An area length error occurred while writing

Global DB, double word access, access address: 65532

OB number: 1

Module Address: 30

Required OB: Programming Error OB (OB121)

OB not found, disabled, or unable to start in current working mode

Internal error, incoming event

08:55:02.726 2011-11-23

The root cause of the error is that MW50 has not been initialized to 0, resulting in a subtraction operation that yields 16#FFFF.

LMW50
L1
-I

The address value generated by the last indirect addressing instruction "TDBD[AR1, P#0.0]" exceeds the defined range of DB1 (which is 200 bytes).

It's important to note that the last instruction must be temporarily commented out using "//" to enable proper monitoring of the program and to identify the issue.

This kind of error is often tricky to detect because the program may run without immediate errors, but the system fails to enter the running mode correctly. Ensuring all instructions are properly commented when debugging can save a lot of time during troubleshooting.