GE PACSystems RX7i - Page 149

Chapter 4. Ladder Diagram (LD) Programming
134 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C
Each counter uses a one-dimensional, three-word array of %R, %W, %P, %L, or symbolic memory to
store the following information:
Current value
(CV)
Word 1
Warning
The first word (CV) can be read but should not be written
to, or the function may not work properly.
Preset value
(PV)
Word 2
When the Preset Value (PV) operand is a variable, it is normally set to a
different location than word 2 in the timer’s or counter’s three-word
array.
■ If you use a different address and you change word 2 directly, your
change will have no effect, as PV will overwrite word 2.
■ If you use the same address for the PV operand and word 2, you can
change the Preset Value in word 2 while the timer or counter is
running and the change will be effective.
Control word
Word 3
The control word stores the state of the Boolean inputs and outputs of
its associated timer or counter, as shown in the following diagram:
Warning
The third word (Control) can be read but should not be
written to; otherwise, the function will not work.
Word 3: Control Word Structure
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Reserved
Q (counter/timer status output)
EN (enable input
Reset input
Enable input, previous execution
Note: Bits 0 through 13 are not used for counters.