Allen-Bradley micrologix 1500 - CTU - Count up CTD

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Publication 1762-RM001C-EN-P

Timer and Counter Instructions 8-9

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.

CTU

Count Up

Counter C5:0

Preset 0<

Accum 0<

CTU

Count Down

Counter C5:0

Preset 0<

Accum 0<

CTD

Table 8.14 Execution Time for the CTU and CTD Instructions

Controller CTU - When Rung Is: CTD - When Rung Is:

True False True False

MicroLogix 1200 9.0

s9.2

s9.0

MicroLogix 1500 6.4

s8.5

s7.5

s8.5

NOTE

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.

Allen-Bradley micrologix 1500 - CTU - Count up CTD - Count down