Instruction manual

Timers
890USE18300 September 2003 123
Rising-edge Timer Block
Summary A rising-edge timer block starts a timing operation when its trigger rises from 0 to 1.
The block 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 rising-edge timer
block is a Boolean that rises to 1 while the timer is accumulating and drops to 0 when
the accumulator is at the terminal count. You may invert the value of the output.
Structure of a
Rising-edge
Timer Block
A block diagram for a standard rising-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 will make
the timer inoperable when it is set to 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 block 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 is a Boolean value. The standard output is 1 while the block is
accumulating counts and 0 when it is not counting. The output may be inverted.
enable
trigger
rising-edge timer
reset
time unit x terminal count
output