Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 145)

Chapter 8
Using Basic Instructions
8–26
Using Status Bits
This Bit Is Set When
And Remains Set Until One
of the Following
Count Down Underflow Bit
UN (bit 11) accumulated value wraps
around to +32,768 (from
–32,767) and continues
counting down from there a RES instruction having the
same address as the CTD
instruction is enabled. OR
the count is incremented
greater than or equal to
+32,767 with a CTU instruction
Done Bit DN (bit 13) accumulated value is equal to
or greater than the preset value the accumulated value
becomes less than the preset
Count Down Enable Bit EN
(bit 14) rung conditions are true rung conditions go false OR
a RES instruction having the
same address as the CTD
instruction is enabled
Entering the Instruction
You enter the instruction from within the program monitor functional area.
P 0 0 0 C T D A D D R
C 1
P 0 0 0 C T D P R E
* * * 1 2 0
P 0 0 0 C T D 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 D C 0 1
P 1 2 0 A 0
The accumulated value is retained after the CTD 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 executed. The CD bits are always set prior to entering the
RRUN, RCSN, or RSSN modes.
6
ENT FUN
To enter the function code, press: