Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 43)

Memory Organization
Chapter 4
4Ć5
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
transfer of output data to output devices occur during I/O scan. If the status of
the output instruction changes in the program then the on or off status of the
output devices update during the I/O scan to reflect the change.
To use the data table, you must understand the following:
The processor initially reserves the first 128 words in the memory for the
data table.
You can decrease the data table size to 48 words in two word increments.
You can increase the data table size to 256 words in two word increments.
Then you can increase the data table size in blocks of 128 words.
When the data table is set to 256 words, you can program up to 104
timer/counter instructions.
You can change the data size from 48 words to 2,944 words using the
1770-T3 terminal.
Data Table Expansion
Using the 1770-T3 industrial terminal, you can adjust the data table size to be
anywhere from 48 words to 2944 words. Expanding the data table provides
additional timers/counters and space for files (see chapter 8 for timers/counters
and chapter 10 for file information), but it also proportionally reduces the
program storage and memory areas.
Expansion is in increments of two words until a table of 256 is reached and then
in increments of 128 words.
Important: When using the data table expansion capability, allow sufficient
room for both data table and user program.