Programming instructions

Chapter 2 Lab and 1200 Devices
DAQ Hardware Overview Guide 2-6 www.ni.com
Lab and 1200 Devices Waveform Generation
The Waveform Generation functions can continuously write values to
either one or both analog output channels using an onboard or external
clock to update the DACs at regular intervals. The values are contained in
a buffer that you allocate and fill. The resultant voltages produced at the
analog output channels depend on the value of the integer numbers in the
buffer, the level of the reference voltage, and the polarity setting.
Lab and 1200 Devices Digital I/O
The Lab and 1200 devices contain 24 bits of digital I/O. These bits are
divided into a set of three digital I/O ports of eight bits each. The Intel
8255A Parallel Peripheral Interface chip controls digital I/O. The
digital I/O ports are labeled as ports PA, PB, and PC on the I/O connectors,
as shown in your device user manual.
You can configure all three ports as either input ports or output ports. These
ports are referred to as ports 0, 1, and 2 for the Digital I/O functions, in
which:
• Port PA = port 0
• Port PB = port 1
• Port PC = port 2
Ports 0 and 1 support both handshaking and no-handshaking modes. Port 2
supports no-handshaking mode only. The digital lines making up port 2
(PC) are used as handshaking lines for both ports 0 and 1 whenever either
is configured for handshaking mode; therefore, port 2 is not available for
Digital I/O functions whenever either port 0 or port 1 is configured for
handshaking mode.
Using a non-remote SCXI chassis with a Lab-PC+ or a DAQCard-1200 or
using an SCXI-1200 in multiplexed mode renders port PB unavailable.
NI-DAQ also reserves line 0 of port PC for input from the SCXI hardware
if you have SCXI configured. The remaining lines of port PC are available
for input only.
Lab and 1200 Devices Groups
You can group any combination of ports 0 and 1 together to make up larger
ports.