Instruction manual

Timers

116

890USE18300 September 2003

Timer Reset

Input

The reset input is essentially a timer override mechanism. It may be a Boolean 1 or

0. The block is operational when the reset value is 1; it does not operate when the

reset value is 0.

The reset input 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

The following timing diagram shows how the value of the reset input effects the

inverted output from the timer block:

At the beginning of the timing sequence, while the reset input is 1, the standard

output is 1 (the inverted output is 0) before and while the block is accumulating. The

standard output goes to 0 (the inverted output goes to 1) when TC is reached. When

the trigger rises to 1, the timer drops to 0, and the standard output rises to 1 (the

inverted output falls to 0).

The second time the trigger input falls to 0, the timer begins to accumulate again.

But before the accumulation completes the second time, the reset input drops to 0,

thereby sending the timer to 0. The standard output remains at 1 (the inverted output

remains at 0).

When the timer trigger value drops to 0 for the third time, the timer begins to

accumulate again. Once TC has been reached, the output drops to 0 again and

stays at 0 as long as the trigger input is 0 and the reset input is 1.

timer trigger

timer

output

reset

output

inverted