Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 35)

Memory Organization
Chapter 4
4Ć6
There are six areas (Figure 4.3) making up the data table. They are:
Input image table
Output image table
Processor work areas (2)
Timer/Counter accumulated values and internal storage
Timer/Counter preset values and internal storage
Chapter 2 discusses the input and output image tables. We will now discuss the
remaining areas. Keep in mind that we are referring to a factory configured
data table.
Processor Word Areas
Purpose: The processor uses these 16 words (addresses 000-007 and 100-107)
for its internal control functions.
Description: There are two processor work areas. They are located at
addresses 000-007 and 100-107. You cannot access these memory locations.
Their word addresses are not available for addressing.
NOTE: The term address is defined in chapter 5. Remember, all addresses are
base eight values.
Accumulated Values and Internal Storage
Purpose: Stores accumulated values of timer or counter instructions. This area
also stores data by words and/or bits from your program instructions.
(Addresses 030-077).
Description: Each timer or counter instruction uses two words of memory.
One word is stored in the accumulated value area, the other is the preset value
area. The preset value is 100* above the accumulated value. Therefore, a
timer/counter having an address of 030 automatically has its preset value stored
at address 130.
Preset Values and Internal Storage
Purpose: Stores preset values (PR) of timer or counter instructions. This area
also stores data by words and/or bits from your program (addresses 130- 177).
Description: The preset value is the number of timed intervals or events to be
counted. When the accumulated value equal the preset value (AC = PR), a
status bit is set and can be examined to turn on or off an output device.
This is the second major part of memory. It is divided into three areas:
Main ladder diagram program
Subroutine area
Data highway instructions
Data Table Areas
User Program