Programming instructions

Chapter 17 Shaking Hands with a Digital Partner
LabVIEW Data Acquisition Basics Manual 17-10
© National Instruments Corporation
Figure 17-9 shows an example of a circular-buffered application. In this
example, you are reading or writing digital values continually until you stop
the VI or an error occurs. In order to create a circular buffer, you must create
a buffer that is at least twice as large as the number of scans/updates you
want to read at a time. You can have an internal or external
handshake
source
. If your
handshake source
is internal, remember to specify the rate
at which you read values with the
clock frequency
.
Scan backlog
specifies
how many values are left in the buffer after you read. The
number read
input indicates the total number of values that have been read from the
buffer because the VI started executing.
Figure 17-9.
Digital Handshaking Using a Circular Buffer
Digital handshaking, whether non-buffered or buffered, inputs or outputs
digital patterns only after your computer receives a digital pulse. Not all
DAQ devices support digital handshaking. The DIO-32 Series devices
have internal as well as external handshaking signals and support
circular-buffered I/O. Other DAQ devices that support handshaking accept
only external handshaking signals. You should use digital handshaking
when you need to generate or retrieve a digital pattern after a digital event,
or pulse, is detected.