Instruction manual

Analog Latches
142
890USE18300 September 2003
High-level Analog Latch Block
Summary A high-level analog latch block produces a latched output when the block’s trigger is
1 and an unlatched output when the trigger is 0. When the block is unlatched, the
value of the output is identical to the value of the analog input. When the block is
latched, the value of the output is latched to the value of the analog input when the
latch trigger rises from 0 to 1. The output is an analog value in the form of a 16-bit
word.
Structure of a
High-level
Analog Latch
Block
A block diagram for a high-level analog latch is shown below:
output equal to the analog input when latch trigger = 0
output latched to the analog input when latch trigger = 1
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 to a value 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 is the value of the block, either latched or unlatched. 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 high-level analog latch 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)
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
high-level analog-latch
analog input