Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 45)

Memory Organization
Chapter 4
4Ć7
Data Table Areas
The following areas make up the data table. They are:
processor work area no. 1
output image table
bit/word storage (020-027)
timer/counter accumulated values and internal storage
processor work area no. 2
input image table
bit/word storage (120-127)
timer/counter preset values and internal storage
Chapter 1 describes the input and output image tables. The following sections
describe the remaining areas.
Processor Work Areas
Purpose: The processor uses these 16 words 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 data table words. Their word
addresses are not available for addressing.
Important: The term address is defined in chapter 6. Remember, all addresses
are in octal 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 data table.
one word is stored in the accumulated value area, the other is the preset value
area. When the accumulated value equals the preset value (AC=PR), a status bit
is set and can be examined to turn on or off an output device.
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. The preset value is 100 octal words above the accumulated word.
Therefore, a timer/counter having an address of 030 automatically has its preset
value stored at address 130.