GENERAL PRESENTATION
WHAT IS AN OBJECT
An object is an entity that can be manipulated by program, it can be an input image, part of a timer, part of the system, part of communication, etc.
REPRESENTATION OF OBJECTS
Objects are represented by the symbol “%” followed by one or two letters specifying their type and then a letter specifying their format (bits, byte, words, double, real etc.)
LIST OF DIFFERENT TYPES OF OBJECTS
DFB types (No format precision)
OBJECT FORMATS
THE ELEMENTS OF OBJECTS
Most objects are made up of several elements or sub-elements, for example, a counter contains a current value, a preset value, two overflow bits and one preset bit reached
Discrete input cards have bits representing the physical states of the sensors, but also a module fault bit and a fault bit per channel, some cards also have words or tables of words representing their states or their configurations.
We access an element of an object by putting a period behind the number of the object then the identifier of the element (a number or a reserved symbol), then if the element contains other sub-elements we add a dot followed by the Identifier etc.
CARD OBJECTS
To identify an object on a card, you must specify its module number then the channel number.
If several objects are associated with a channel, the object number must be specified. (except for object N ° 0)
Examples:% IW0.12.2 Word 2 of channel 12 of module 0
% IW0.12 Word 0 of channel 12 of module 0
STRUCTURED OBJECTS
(bits extracted from words, tables of bits, tables of words)
BIT EXTRACT FROM WORDS
BIT TABLES OR BIT STRINGS
TABLE OF WORDS
Example objects of an entry card at slot 4
FORMS OF ADDRESSING
DIRECT ADDRESSING
Example of direct address:% MW20
The address is fixed, and defined by program.
THE INDEX ADDRESS
The direct address is completed with an index, contained in a word.
EXERCISE 1 ADDRESSING OBJECTS
