Instruction manual

Timers
890USE18300 September 2003 115
Enable Input A delay-to-stop timer block can be enabled either by a Boolean 1 or an always
enabled constant. It can be disabled by a Boolean 0 or an always disabled constant.
If the enable input is a Boolean, it may be produced by:
a digital input from a module on the island
a digital output from the virtual module (See The Virtual Module, p. 28)
an output on the action module (See Using the Action Module as an Input to a
Block, p. 32) written to by the fieldbus master
When the enable input is a Boolean 0 or an always disabled constant, the block is
disabled. The timer finishes a timing cycle if it has already started it, but it does not
change the output—the output is frozen in the state it was in when the block became
disabled. The block continues to process inputs but does not act on them. If the
block becomes enabled, it immediately begins acting on the latest set of inputs
received.
Timer Trigger
Input
The falling edge of the trigger input starts a timing operation, and the rising edge of
the trigger input causes the timer accumulator to drop to 0. The trigger input may be
a Boolean 1 or 0.
For a delay-to-stop timer block, the value of the trigger input is important for the
output from the block. If the trigger rises to 1 before the timer reaches the terminal
count, the timer stops accumulating and drops to 0. When this happens, the output
never turns off. If the trigger remains at 0 after the terminal count has been reached,
the timer accumulator holds the terminal count value and the output turns off.
The timer trigger value may be produced by:
a constant
a digital input from a module on the island
a digital output from the virtual module (See The Virtual Module, p. 28)
an output on the action module (See Using the Action Module as an Input to a
Block, p. 32) written to by the fieldbus master
if the timer is the second part of a nested reflex action (See Nesting Two Reflex
Blocks, p. 36), its trigger input may be configured as the output of the first reflex
action