DAQ VXI-SC-1102 Manual de Instruções descarregar pdf (Página 100)

Chapter 15 VXI-DAQ Devices

DAQ Hardware Overview Guide 15-2 www.ni.com

Note Unpredictable behavior can result if other VXIbus devices simultaneously use the

same VXIbus trigger line the VXI-MIO devices are using to synchronize their operations.

VXI-DIO-128 Digital I/O Device

The VXI-DIO-128 is a 128-channel parallel digital I/O module for

the VXIbus. The module uses eight 16-bit programmable peripheral

interfaces (PPIs) that can be subdivided further into 16 8-bit ports. Four

82C55 PPI chips control 64 open-drain output channels. Four 82C55 PPI

chips control 64 input channels with programmable thresholds. These

16 ports are referred to as ports 0 through 15 by the Digital I/O functions.

You can configure ports 0 through 7 only as input ports. The threshold

voltage for each of these input ports you can program independently by

selecting a voltage between −32 and +31.75 V in 250 mV steps. By

comparing the input digital signal to the threshold values, the module can

translate the input voltage levels above the threshold to active high readings

and below the threshold to active low readings.

You can configure ports 8 through 15 only as output ports. However, each

of these ports is equipped with read-back capability. Each output line has

built-in transient suppression diodes, which protect against the voltage

spikes that are generated when relays turn off and on. Writing 1 to a given

line turns the relay driver on, which grounds the output pin. Thus, when you

use a line as a general-purpose output, an inversion occurs.

VXI-AO-48XDC Analog Output Device

The VXI-AO-48XDC is a precise DC setpoint module for the VXIbus. This

module contains 48 voltage outputs plus 48 separate current outputs for a

total of 96 analog output channels with 18-bit DAC resolution. Each one of

these channels is independently programmable. The channel numbering is

0 through 47, with each channel controlling a pair of voltage and current

outputs. Whether a channel controls its voltage or current output is

determined by a call to NI-DAQ function

AO_Change_Parameter or the

LabVIEW

AI_Config.vi or AO_Hardware_Config.vi.

The VXI-AO-48XDC has one 18-bit DAC that is time-division multiplexed

to create the 48 voltage output channels and the 48 current output channels.

The channel data is stored in nonvolatile RAM. This feature enables the

module to support the following two update modes: update when written to

and later internal update mode. Furthermore, this design allows power on

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