Publication 1763-RM001C-EN-P - October 2009
Timer and Counter Instructions
177
CTU - Count Up
CTD - Count Down
Instruction Type: output
The CTU and CTD instructions are used to increment or decrement a
counter at each false-to-true rung transition. When the CTU rung makes a
false-to-true transition, the accumulated value is incremented by one
count. The CTD instruction operates the same, except the count is
decremented.
CU
DN
CTU
Count Up
Counter
C5:0
Preset
0<
Accum
0<
CTU
CU
DN
CTU
Count Down
Counter
C5:0
Preset
0<
Accum
0<
CTD
Execution Time for the CTU and CTD Instructions
Controller
CTU - When Rung Is:
CTD - When Rung Is:
True
False
True
False
MicroLogix 1100
2.28
μ
s
2.15
μ
s
2.24
μ
s
2.09
μ
s
TIP
If the signal is coming from a field device wired to an
input on the controller, the on and off duration of the
incoming signal must not be more than twice the
controller scan time (assuming 50% duty cycle). This
condition is needed to enable the counter to detect
false-to-true transitions from the incoming device.
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive