Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 144)

Chapter 8
Using Basic Instructions
8–25
Entering the Instruction
You enter the instruction from within the program monitor functional area.
P 0 0 0 C T U A D D R
C 0
P 0 0 0 C T U P R E
* * * 1 2 0
P 0 0 0 C T U A C C
* * * * * 0
Once instruction entry is complete, the parameters are condensed to one
screen as shown here:
P 0 0 0 C T U C 0 0
P 1 2 0 A 0
The accumulated value is retained after the CTU instruction goes false or
when power is removed from and then restored to the controller. Also, the
on or off status of counter done, overflow, and underflow bits is retentive.
The accumulated value and control bits are reset when the appropriate RES
instruction is enabled. The CU bits are always set prior to entering the
RRUN, RCSN, or RSSN modes.
The CTD is a retentive output instruction that counts false-to-true rung
transitions. Rung transitions can be caused by events occurring in the
program such as parts traveling past a detector or actuating a limit switch.
When rung conditions for a CTD instruction have made a false-to-true
transition, the accumulated value is decremented by one count, provided that
the rung containing the rung containing the CTD instruction is evaluated
between these transitions.
The accumulated counts are retained when the rung conditions again become
false. The accumulated count is retained until cleared by a reset (RES)
instruction that has the same address as the counter reset.
ENT
5
To enter the function code, press:
FUN
(CD)
(DN)
CTD
COUNT DOWN
Counter
C5:1
Preset 120
Accum 0
Execution Times (
µ
sec) when:
True False
32.19 27.22
Ladder representation:
Count Down (CTD)