Rockwell Automation Logix5000 Controllers Controller Information and Status Programming Manual - Manual (Page 21)

Determine controller memory information Chapter 2
Choose the memory information
The MSG instruction returns the following information to INT_array
(destination tag of the MSG).
Important: The controller returns the values in 32-bit words. To see a value in bytes, multiply it by 4. If your controller
does not divide its memory, the values show up as I/O memory. For the 1756-L55M16 controller, the MSG
instruction returns two values for each logic memory category. To determine the free or total logic memory
of a 1756-L55M16 controller, add both values for the category.
If you want the Then copy these array
elements
Description
Amount of free I/O memory (32-bit
words)
INT_array[3] Lower 16 bits of the 32 bit value
INT_array[4] Upper 16 bits of the 32 bit value
Amount of free data and logic memory
(32-bit words)
INT_array[5] Lower 16 bits of the 32 bit value
INT_array[6] Upper 16 bits of the 32 bit value
1756-L55M16 controllers only—
amount of additional free logic memory
(32-bit words)
INT_array[7] Lower 16 bits of the 32 bit value
INT_array[8] Upper 16 bits of the 32 bit value
Total size of I/O memory (32-bit words) INT_array[11] Lower 16 bits of the 32 bit value
INT_array[12] Upper 16 bits of the 32 bit value
Total size of data and logic memory (32-
bit words) INT_array[13] Lower 16 bits of the 32 bit value
INT_array[14] Upper 16 bits of the 32 bit value
1756-L55M16 controllers only—
additional logic memory (32-bit words)
INT_array[15] Lower 16 bits of the 32 bit value
INT_array[16] Upper 16 bits of the 32 bit value
1756-L55M16 controllers only—largest
contiguous block of additional free logic
memory (32-bit words)
INT_array[19] Lower 16 bits of the 32 bit value
INT_array[20] Upper 16 bits of the 32 bit value
Largest contiguous block of free I/O
memory (32-bit words) INT_array[23] Lower 16 bits of the 32 bit value
INT_array[24] Upper 16 bits of the 32 bit value
Largest contiguous block of free data
and logic memory (32-bit words) INT_array[27] Lower 16 bits of the 32 bit value
INT_array[28] Upper 16 bits of the 32 bit value
Rockwell Automation Publication 1756-PM015F-EN-P – October 2014 21