Instruction manual

Timers
890USE18300 September 2003 125
Enable Input A rising-edge 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 timer trigger is essentially a timer start command. It may be a Boolean 1 or 0.
The timer starts accumulating time units when the timer trigger rises from 0 to 1.
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 block in a nested reflex action (See Nesting Two Reflex
Blocks, p. 36), its trigger input may be configured as the output of the first reflex
block
Note: At start-up, make sure that the trigger input provides a 0 to the timer block.
If the trigger is 1 when the timer becomes enabled, the block will assume that a
rising edge transition has just taken place and will start accumulating time counts
immediately. If the trigger input is 0 when the timer becomes enabled, the block will
wait for the next rising edge transition before it starts the time-unit accumulation.