Rockwell Automation D64046.5.1 U MNL WIN DDMC - Manual (Page 147)

Reference Information
Appendix A
A-3
Step Description File Size Requirements
Table A.E lists the number of words needed for each step in the step
description file for an SDS instruction with 8, 16, and 32 I/O.
Table A.E
Step Description File Size Requirements (for both PLC-5 and PLC-5/250)
Number of I/O Number of Words Needed for Each Step in Step
Description File
8 13
16 22
32 43
Determining Amount of Data Table Memory Needed for SDS
Instructions
When used for control and diagnostics (as opposed to monitoring-only),
the SDS instruction requires at least twice as much memory as the original
ladder logic. You must take this into account when planning your
program.
To calculate the amount of memory required for an SDS instruction, use
the following formula:
size of control file + ((number of steps defined) x words needed per
step)
For example, consider that we have 4 SDS instructions in the PLC-5 with
10 steps each. Each instruction has 8 inputs and 8 outputs:
68 words needed for control file + (10 steps x 13 words needed per
step) =
198 words per SDS x 4 SDS instructions =
792 words of data table memory
Determining Amount of Program File Memory Needed for SDS CAR
File
An SDS instruction uses program memory for the contents of the CAR file.
(The SDS CAR uses 1267 words of program memory in the PLC-5 processor
and 1280 words of program memory in the PLC-5/250 processor.) The total
amount of program memory used is different depending on if you are using a
PLC–5 processor or a PLC-5/250 processor.