Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 41)

Data Table
Chapter 3
3Ć14
After the number of I/O racks is selected, the industrial terminal will
compute and enter the data table size.
Anytime you reduce the size of the data table, the processor searches
for instructions in those areas. If an instruction exists in an area to be
deleted, the change will not be allowed and the following message will be
displayed: “INSTRUCTION EXISTS IN DELETED AREA.” To display
the rung that is preventing the change, press [SEARCH]. At that time, the
decision can be made whether to keep or delete the instruction.
Anytime you increase the size of the data table, the user program is
automatically moved into higher word addresses. However, once the
memory is full, expansion is not permitted and the message “MEMORY
FULL” is displayed. Press [CANCEL COMMAND] to terminate the data
table configuration display (Table 3.A).
Changing Data Table Areas
You may reduce data table size from the standard or default value of 128
words to 48 words when 8 timers/counters and one I/O rack are being
used. This assumes 8 words are reserved in both the input and the output
image table. Additional space is then made available for user program
instructions. Reductions can be made in decrements as small as two words
(one timer/counter). If the memory locations are occupied, the attempted
reduction fails.
You can increase data table size from 128 to 256 words, also in increments
of two words (one timer/counter). This provides up to 104 timers/counters
with 16 words reserved for each input/output image table. Above 256,
data table size is increased in sections of 128 words. You therefore gain the
use of an additional 128 words (64 timer/counter instruction addresses or
128 words for bit/word or file storage, or a combination of both) for each
expansion.
The processor determines whether sufficient unused memory remains for
the corresponding shifting of user program instructions from the area to be
addressed by the additional address area. If sufficient memory exists, the
required number of words are than reserved.
Input/Output Image Table Sizes
You may optionally alter the number of words reserved for input/output
image tables. Memory can be changed from 128 to 896 I/O, in increments
of 128 I/O (i.e., 1 rack).
By reducing memory areas required for inputs/outputs from 256 to 128
(from 2 racks to 1 rack), data table size remains unchanged, but an