Timer Instructions Overview - Allen-Bradley MicroLogix 1400 Instruction Manual

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Timer Instructions
Overview
175
Timer and Counter Instructions
Timers and counters are output instructions that let you control operations
based on time or a number of events. The following Timer and Counter
Instructions are described in this chapter:
Instruction
TON - Timer, On-Delay
TOF - Timer, Off-Delay
RTO - Retentive Timer On
CTU - Count Up
CTD - Count Down
RES - Reset
For information on using the High-Speed Counter output(s), see Using the
High-Speed Counter and Programmable Limit Switch on page 99.
Timers in a controller reside in a timer file. A timer file can be assigned as
any unused data file. When a data file is used as a timer file, each timer
element within the file has three sub-elements. These sub-elements are:
• Timer Control and Status
• Preset - This is the value that the timer must reach before the timer
times out. When the accumulator reaches this value, the DN status
bit is set (TON and RTO only). The preset data range is from
0...32767. The minimum required update interval is 2.55 seconds
regardless of the time base.
• Accumulator - The accumulator counts the time base intervals. It
represents elapsed time. The accumulator data range is from
0...32767.
Timers can be set to any one of three time bases:
Used To:
Delay turning on an output on a true rung
Delay turning off an output on a false rung
Delay turning on an output from a true rung.
The accumulator is retentive.
Count up
Count down
Reset the RTO and counter's ACC and status
bits (not used with TOF timers).
Publication 1766-RM001A-EN-P - October 2008
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