Rockwell Automation 2080-LC20-20QBBR Micro820 20-point Programmable Controllers User Manual - Manual (Page 59)

Rockwell Automation Publication 2080-UM005A-EN-E - December 2013
51
Chapter
6
Program Execution in Micro800
This section provides a brief overview of running or executing programs with a
Micro800 controller.
Overview of Program
Execution A Micro800 cycle or scan consists of reading inputs, executing programs in
sequential order, updating outputs and performing housekeeping (datalog, recipe,
communications).
Program names must begin with a letter or underscore, followed by up to 127
letters, digits or single underscores. Use programming languages such as ladder
logic, function block diagrams and structured text.
Up to 256 programs may be included in a project, depending on available
controller memory. By default, the programs are cyclic (executed once per cycle or
scan). As each new program is added to a project, it is assigned the next
consecutive order number. When you start up the Project Organizer in
Connected Components Workbench, it displays the program icons based on this
order. You can view and modify an order number for a program from the
program’s properties. However, the Project Organizer does not show the new
order until the next time the project is opened.
The Micro800 controller supports jumps within a program. Call a subroutine of
code within a program by encapsulating that code as a User Defined Function
Block (UDFB). Although a UDFB can be executed within another UDFB, a
maximum nesting depth of five is supported. A compilation error occurs if this is
exceeded.
Alternatively, you can assign a program to an available interrupt and have it
executed only when the interrupt is triggered. A program assigned to the User
Fault Routine runs once just prior to the controller going into Fault mode.
In addition to the User Fault Routine, Micro800 controllers also support two
Selectable Timed Interrupts (STI). STIs execute assigned programs once every
set point interval (1…65535 ms).
The Global System Variables associated with cycles/scans are:
• __SYSVA_CYCLECNT – Cycle counter
IMPORTANT
This section generally describes program execution in Micro800
controllers. Certain elements may not be applicable or true in certain
models (for example, Micro820 does not support PTO motion control).