Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 33)

Data Table
Chapter 3
3Ć6
CAUTION: Word 027 is reserved for processor use. Do not put
block transfer or output modules in rack 2, I/O group 7.
Timer/Counter Accumulated Values, Bit/Word Storage
This area of memory is used to store accumulated values of timer/counter
instructions. The area may also be used as storage for words and/or bits.
Word addresses 030
8
to 077
8
bound this area when memory is configured
for 256 I/O (maximum) and 40 Timer/Counter Instructions (Figure 3.3).
NOTE: Each timer or counter used actually requires two words of data
table memory: one from the accumulated value area (030
8
to 077
8
) and the
other from the preset value area (130
8
to 177
8
).
Input Image Table
The input image table duplicates the status of the inputs wired to input
modules. If an input is on, its corresponding input image table bit is set
to on. If an input is off, its corresponding bit in memory is cleared to off.
These bits are monitored by instructions in the user program.
Input image table bits are updated each scan cycle to correspond to the
information supplied by input modules.
The input image table is bounded by word addresses 110
8
to 127
8
(Figure 3.3). This area contains 16 word addresses, or 256 bit addresses.
With the industrial terminal, the input image table can be reduced to 8
word addresses (128 bit addresses), or increased to 56 word addresses
(896 bit addresses). By changing memory configuration to 896 I/O (seven
1771-A4B I/O chassis), the 896 bit addresses represent the maximum
number of discrete inputs the processor can monitor.
In a local PLC-2/30 controller, the total bits used, which represent actual
hardware inputs and outputs together, cannot exceed 896 I/O. This number
represents the maximum I/O capability of the PLC-2/30 Programmable
Controller and is possible only when the system is programmed with the
1770-T3 or 1784-T50 industrial terminal.