ContentsGFK-0467K vii
Chapter 1 Introduction......................................................................................................... 1-1
Additional Reference Information: See the appendices in the back of this manual....1-2
Chapter 2 System Operation................................................................................................ 2-1
Section 1: PLC Sweep Summary..................................................................... 2-2
Standard Program Sweep.................................................................................................. 2-2
Sweep Time Calculation.............................................................................................2-6
Housekeeping.............................................................................................................2-6
Input Scan..................................................................................................................2-7
Application Program Logic Scan or Solution.............................................................2-8
Output Scan................................................................................................................2-9
Logic Program Checksum Calculation.......................................................................2-9
Programmer Communications Window............................................................................2-9
System Communications Window (Models 331 and Higher)....................................... 2-10
PCM Communications with the PLC (Models 331 and Higher)...................................2-12
Standard Program Sweep Variations.............................................................................. 2-13
Constant Sweep Time Mode ....................................................................................2-13
PLC Sweep When in STOP Mode........................................................................... 2-13
Communication Window Modes..............................................................................2-14
Key Switch on 350 and 360 Series CPUs: Change Mode and Flash Protect .................2-14
Using the Release 7 and Later Key Switch.............................................................. 2-14
Clearing the Fault Table with the Key Switch......................................................... 2-14
Enhanced Memory Protect with Release 8 and Later CPUs.................................... 2-15
Section 2: Program Organization and User References/Data..................... 2-16
Subroutine Blocks (Series 90-30 PLC only)...................................................................2-16
Examples of Using Subroutine Blocks.....................................................................2-18
How Blocks Are Called............................................................................................2-19
Periodic Subroutines.................................................................................................2-19
User References.............................................................................................................. 2-20
Transitions and Overrides...............................................................................................2-21
Retentiveness of Data .....................................................................................................2-21
Data Types...................................................................................................................... 2-23
System Status References............................................................................................... 2-24
Function Block Structure................................................................................................ 2-26
Format of Ladder Logic Relays................................................................................2-26
Format of Program Function Blocks........................................................................ 2-27
Function Block Parameters............................................................................................. 2-28
Power Flow In and Out of a Function......................................................................2-29
Section 3: Power-Up and Power-Down Sequences ......................................2-30
Power-Up........................................................................................................................ 2-30
Power-Down ...................................................................................................................2-33