Instruction manual

Analog Latches
130
890USE18300 September 2003
Falling-edge Analog Latch Block
Summary A falling-edge analog latch block produces an output that latches the value of an
analog input when the trigger drops from 1 to 0. The output remains latched while
the trigger is at 0 and while it transitions back to 1. If the latch trigger transitions from
1 to 0 again, the block latches the output to the value of the analog input at the time
of the second transition. The output is always a latched analog value in the form of
a 16-bit word.
Structure of a
Falling-edge
Analog Latch
Block
A block diagram for a falling-edge analog latch is shown below:
output latched to the value of the analog input at the latest falling edge of the latch trigger
The latch block has three inputs—an enable input, a latch trigger and an analog
input. The enable input turns the block on or off. The latch trigger causes the block
to latch onto the value of the analog input at the moment that it transitions from 1 to
0. The analog input is an integer value that is latched when the trigger fires. It may
be an unsigned integer value in the range 0 to 65 535 or a signed integer value in
the range -32 768 to +32 767.
The output of the block is the latched value. It may be an unsigned integer value in
the range 0 to 65 535 or a signed integer value in the range -32 768 to +32 767.
Enable Input A falling-edge analog latch 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)
When the enable input is a Boolean 0 or an always disabled constant, the block is
disabled—the action does not execute and 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.
output
enable
latch trigger
falling-edge analog latch
analog input