Installation manual

Publication 1747-RM001G-EN-P - November 2008
E-14 Data File Organization and Addressing
Effects of Program Interrupts on Index Register S:24
When normal program operation is interrupted by the user error handler, an
STI, or an I/O interrupt, the content of index register S:24 is saved; then,
when normal program operation is resumed, the content of index register S:24
is restored. This means that if you alter the value in S:24 in these interrupt
subroutines, the system will overwrite your alteration with the original value
contained on subroutine entry.
Specifying an Indirect Address
Indirect addressing allows you to write less complex ladder logic programs and
saves you memory space. You have the option of using word-level and
bit-level indirect addresses when using an SLC 5/03 (OS302), SLC 5/04
(OS401), and SLC 5/05 processors. Indirect bit addresses are based on the
form of the indirect address and the type of bit instruction.
Use indirect addressing for applications such as indexing sequential batch files
in a multiple batch operation. For example, at completion of each operation,
let a counter accumulated value call out the next batch file, such as:
N10, N11, N12,...N[C5:0.ACC].
When you specify indirect addresses, follow these guidelines.
• You can indirectly address:
– file number.
– word number (element
+ sub-element).
– bit number (in a binary file).
• The substitute address must be any address specified to the word level.
• Enter the substitute address in brackets [ ].