©
National Instruments Corporation
2-1
2
Device Overview
This chapter provides information abo
u
t NI 660
x
device f
u
nctionality.
Digital I/O
The NI 660
x
devices have a 32-bit DIO port on PFI <0..31>. Digital I/O
consists of asynchrono
u
s reads and writes to the digital port
u
pon software
command. Yo
u
can individ
u
ally config
u
re each line for digital inp
u
t or
o
u
tp
u
t. For o
u
tp
u
t, yo
u
can individ
u
ally config
u
re PFI <8..31> for either
co
u
nter-associated o
u
tp
u
t or digital o
u
tp
u
t. Yo
u
m
u
st specify whether yo
u
are
u
sing the PFI line for co
u
nter I/O or digital I/O only if that line is being
u
sed as an o
u
tp
u
t. For inp
u
t, both co
u
nter I/O and digital I/O can share the
lines on PFI <0..31>.
For more information abo
u
t the signals that can be driven onto PFI lines,
refer to the
section of this doc
u
ment.
For information abo
u
t how to implement specific digital I/O f
u
nctions,
refer to the application software doc
u
mentation.
Prescaling
Prescaling allows the co
u
nter to co
u
nt a signal that is faster than the
maxim
u
m timebase of the co
u
nter. The co
u
nters on the NI 660
x
offer
8X and 2X prescaling on each co
u
nter (prescaling can be disabled).
Each prescaler consists of a small, simple co
u
nter that co
u
nts to eight
(or two) and rolls over. This co
u
nter is specifically designed for this
application and can co
u
nt signals that are faster than the general p
u
rpose
co
u
nters. The Ctr
n
So
u
rce signal on the general p
u
rpose co
u
nter will be the
divided signal from the simple co
u
nter.
