Instruction manual

Digital Latches

162

890USE18300 September 2003

Operational

Input

The operational input is a stream of Boolean 1s and 0s that will be latched and

unlatched by the trigger value. It 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 latch is the second block in a nested reflex action (See Nesting Two Reflex

Blocks, p. 36), the latch trigger input may be the output from the first reflex block

The following timing diagram shows how the value of the trigger effects the output

from the block:

At the beginning of the timing sequence, the standard output echoes the value of the

operational input (the inverted output echoes the inverse of the operational input) as

long as the trigger is low. When the trigger transitions from 0 to 1 the first time, the

operational input is low. The trigger latches the standard output at 0 (the inverted

output at 1), and holds it there as long as the trigger stays high.

At the moment when the latch trigger transitions back to 0, the standard output

begins to echo the operational input again (the inverted output echoes the inverse

of the operational input again).

When the latch trigger transitions from 0 to 1 the second time, the operational input

is high. The trigger latches the standard output at 1 (the inverted output at 0).

operational input

latch_trigger

output

inverted