GE PACSystems RX7i

Chapter 4. Ladder Diagram (LD) Programming
218 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual GFK-2950C
Warning
Do not use two consecutive words (registers) as the
starting addresses of two timers. Logic Developer - PLC
does not check or warn you if register blocks overlap.
Timers will not work if you place the current value of a
second timer on top of the preset value for the
previous timer.
Word 1: Current value (CV)
Warning
The first word (CV) can be read but should not be
written to, or the function may not work properly.
Word 2: Preset value (PV)
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.
Word 3: Control word
The control word stores the state of the Boolean inputs and outputs of its associated timer or
counter, as shown in the following diagram:
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
Warning
The third word (Control) can be read but should not be
written to; otherwise, the function will not work.
Note: Bits 0 through 13 are used for timer accuracy.