Instruction manual

Timers
118
890USE18300 September 2003
Falling-edge Timer Block
Summary A falling-edge timer block starts a timing operation when its trigger falls from 1 to 0.
The timer needs to be preset to accumulate at a user-specified time unit for a
specified number of counts (the terminal count). The output from a falling-edge timer
block is a Boolean that goes to 1 while the timer is accumulating and 0 when the
timer is not accumulating time units (when the accumulator is at the terminal count).
Optionally, you may invert the value of the output.
Structure of a
Falling-edge
Timer Block
A block diagram for a standard falling-edge timer is shown below:
The timer block has three inputs—an enable input, a timer trigger and a reset. The
enable input allows or stops the output from being updated. The timer trigger is
essentially a timer start command. The reset input is a Boolean value that stops the
timer operation when it is 0.
The block also has two preset values (See Configuring Preset Values for a Reflex
Block, p. 27)—a time unit and a terminal count. The time unit needs to be specified
as some number of ms. The terminal count is a user-defined number of time units.
When a timing operation starts, it will accumulate time units from 0 up to the terminal
count. While the timer is counting, the output turns on. As soon as the timer reaches
the terminal count, the output turns off and remains off until the trigger starts a new
counting sequence.
The output value is a Boolean. The standard output is 1 while the timer is
accumulating counts and 0 when it is not counting. The output may be inverted.
enable
trigger
falling-edge timer
reset
time unit x terminal count
output