USER MANUAL APS 6.0

Preface
Advanced Programming Software User Manual
6–20
Creating and Deleting Data Files
(SLC 500 Processors Only)
When you assign an address to an instruction in your ladder program, you are
allocating memory space to a data file. As more and more addresses are assigned,
the various data files increase in size, according to the needs of your program.
Memory space is allocated in element blocks, beginning with element 0. For
example, suppose the first address you assign in your program is B3/19. This
allocates two elements to your program: B3:0, which consists of bits B3/0 through
B3/15; and B3:1, which consists of bits B3/16 through B3/31. Since B3/16 is the
first bit of element B3:1, all 16 bits of that element are created; therefore, the
highest bit address now available to you is B3/31.
Timers are 3-word elements. If the first timer element you assign in your program
is T4:99, you allocate timers T4:0 through T4:99. By assigning timer T4:100, you
allocate 100 elements using 300 words of memory. So whether you use timers T4:0
through T4:98 later in the program, they are permanently allocated in memory.
Obviously, you can keep the size of your data files to a minimum by assigning
addresses beginning at element 0 of each data file, and trying to avoid creating
blocks of addresses that are allocated but unused.
Note Refer to the Instruction Set Refer ence Manual for detailed information about
addressing and the processor memory layout.
Using Indirect Addresses
Memory
space is allocated for components within indirect addresses. For example,
the address N1 1:[N22:33]/[N44:55] allocates the following space in the data table:
• N11:0/0
• N22:33/0
• N44:55/0
Using Indexed Addresses
Data
tables are not expanded automatically to accommodate indexed addresses.
You must create this data using the memory map function (described in the next
section).