Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual User Manual
Page 31
Data Table
Chapter 3
3Ć4
The first 128 words of the memory are set aside for data table storage.
This number includes 32 words for I/O image tables (i.e., 2 full racks),
16 words for processor work areas and 80 words for timers/counters. If
timers/counters are not required, you can reduce the data table to 48 words.
Expansion is in increments of two words until a table of 256 is reached,
and then in increments of 128 words. The data table can be adjusted to
accommodate the full I/O capacity of the PLC-2/30 processor.
NOTE: The data table expansion capability should be utilized practically.
The user should allow sufficient room for both data table and user
program.
When the data table is set to 256 words, up to 112 timer/counter
instructions can be programmed or 224 storage words are available. Users
can also tail or data table input/output capacity in increments of 128 I/O up
to 896 I/O.
The function of the data table may be explained in relation to inputs and
outputs. Discrete input and output modules cannot store information.
Discrete input and output modules cannot store information. They contain
interface circuits only. Input/output status information (on/off) is actually
stored in memory areas called I/O image tables. An image is defined as an
exact duplicate array of information, that is, the states stored in a different
medium.
Data Table Areas
The data table of the PLC-2/30 programmable controller can be divided
into six distinct areas, assuming default data table size has not been
changed (Figure 3.3). These areas are:
Processor work area 1
Output image table
Timer/counter accumulated values or bit/word storage
Processor work area 2
Input image table
Timer/counter preset values or bit/word storage
The data table area has a default size of 128 words and is configurable
from 48 up to 8,064 words (with 8K word memory) or 8,192 words (with
the 16K word memory). This area stores the information needed in the
execution of the user program, such as input and output device status,
3-digit numeric values, and the status of internal storage points.
Processor Work Areas 1 and 2
There are two processor work areas: processor work area no. 1 (addresses
000
8
to 007
8
) and processor work area no. 2 (addresses 100
8
to 107
8
).