Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 32)

Memory Organization
Chapter 4
4Ć3
Conclusion: 128 I/O is the combined amount of usable bits utilized in the input
image table and/or the output image table.
Memory is divided into three major sections: data table, user program, and a
message storage area. These areas store input status, output status, your
program instructions, and messages.
Figure 4.2 shows these areas with their corresponding octal addresses. We will
describe these areas in detail so you will gain programming flexibility using
your system.
NOTE: Octal is referred to as a base eight numbering system. It is defined in
the glossary.
Figure 4.2
The Areas of Memory
Memory
Data Table
User
Message
Octal
000
177
Varies
3777
Word Addresses
(Varies)
Program
Area
10147-I
Data Table
When we ship your processor, Allen-Bradley sets the memory for specific
addresses. We call this type of data table organization, factory configured.
Figure 4.3 shows memory structure with a factory configured data table. When
we explain specific concepts about the different areas of memory, we will refer
to a factory configured data table.
The data table area is a major part of memory. it is divided into six sections
which includes the input and output image tables. (These two areas were
described in chapter 2). The processor controls and utilizes words stored in the
data table. The input devices coupled with the control logic from your program
determines the status of the output devices. Input devices are limit switches,
pushbutton switches, pressure switches, etc...Output devices are solenoids,
motor starters, alarms, etc... Transfer of input data from input devices and the
Memory