User Guide

Program Methodology—Introduction to PPCL
Siemens Building Technologies, Inc. 1-3
Introduction to PPCL
Imagine trying to control the environment of a 40-story building
without the use of a computer. Suddenly, a large number of daily
functions that are controlled by computers would have to be
controlled by hand. For example, to prepare the building for daily
occupancy, you would have to go to every floor and manually adjust
the setpoint for each control device.
Even though computers are very powerful devices, they need
instructions in order to process information correctly. The instructions
that the computer uses are in the form of a programming language.
The programming language used with the APOGEE Automation
System is called Powers Process Control Language (PPCL).
PPCL is a high-level language developed specifically to control
Heating, Ventilating, and Air Conditioning (HVAC) equipment; it uses
a text-based programming structure like BASIC.
There is much more to writing a PPCL program than putting
instructions and commands together.
• Programs should be logically thought out and their processes
understood before writing program code.
• Programs can be organized differently, but still perform the same
function.
• Although certain programming techniques can work better than
others, no one program is the best solution.
APOGEE PPCL User’s Manual
1-4 Siemens Building Technologies, Inc.
PPCL Rules
Just as grammatical rules are used for the spoken language, PPCL
uses rules to create commands and instructions. Each PPCL
program must conform to these rules; otherwise, the computer will
not understand what you are trying to say.
• Program lines are executed in ascending order according to their
line numbers, unless directed otherwise.
• When the last line of the program is reached, the computer
automatically returns to the first line of the program and continues
processing.
General PPCL Rules
The general rules for PPCL are as follows:
• Each PPCL program contains one or more PPCL statements.
• Each PPCL statement must be assigned a unique line number.
Valid program line numbers are 1 through 32,767.
• The maximum number of program lines a device can contain is
limited to the amount of free memory of that device.
• When transferring program control from a subroutine, you must
use the RETURN command.
• For APOGEE firmware only, each field panel running PPCL
contains one or more separate programs.
• For APOGEE firmware only, the last line of the program does not
need to be executed on every pass of the program. For Unitary
and pre-APOGEE firmware, the last line of the program must be
executed on every pass of the program.
Maximum Number of Characters per Program Line
APOGEE and BACnet Firmware
When entering program lines through an APOGEE field panel HMI or
MMI port, the maximum number of characters per line is 66
(including the line number).