Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 16)

Understanding Your System
Chapter 1
1-6
Classic PLCĆ5 Family Processor Features
From the family of PLC-5 processors, you can choose the processor(s)
that you need for your application. Features common to all Classic PLC-5
processors are:
same physical dimensions
use of the left-most slot in the 1771 I/O chassis
can use any 1771 I/O module in the processor-resident local I/O chassis
with up to 32 points per module
same programming software and programming terminals
same base set of instructions
ladder programs and SFCs can be used by any of the PLC-5 processors
Check with your Allen-Bradley sales office or distributor if you have
questions regarding any of the features of your PLC-5 processor.
Subprogram Calls
Use a subroutine to store recurring sections of program logic that can be
accessed from multiple program files. A subroutine saves memory
because you program repetitive logic only once. The JSR instruction
directs the processor to go to a separate subroutine file within the logic
processor, scan that subroutine file once, and return to the point
of departure.
For detailed information about how you generate and use subroutines, see
your programming software documentation set.
Sequential Function Charts
Use SFCs as a sequence-control language to control and display the state
of a control process. Instead of one long ladder program for your
application, divide the logic into steps and transitions. A step corresponds
to a control task; a transition corresponds to a condition that must occur
before the programmable controller can perform the next control task. The
display of these steps and transitions lets you see what state the machine
process is in at a given time.
For detailed information about how you generate and use SFCs, see you
programming software.
Ladder Logic Programs
A main program file can be an SFC file numbered 1-999; it can also be a
ladder-logic file program numbered 2-999 in any program file.