Bus Mastering Dma; Analog Input; Analog Input Scanning; Analog Output - Measurement Computing PCI-2517 User Manual

PCI-2517 User's Guide

Bus mastering DMA

The PCI-2517 supports bus mastering DMA. With multiple DMA channels, analog, digital, and counter input
data, as well as digital output data, can flow between the PC and the PCI-2517 without consuming valuable
CPU time. The driver supplied with the PCI-2517 automatically uses bus mastering DMA to efficiently conduct
I/O from the PC to the PCI-2517.

Analog input

The PCI-2517 has a 16-bit, 1-MHz A/D coupled with 16 single-ended or eight differential analog inputs. Seven
software programmable ranges provide inputs from ±10 V to ±100 mV full scale.

Analog input scanning

The PCI-2517 has several scanning modes to address various applications. You can load the 512-location scan
buffer with any combination of analog input channels. All analog input channels in the scan buffer are measured
sequentially at 1 µs per channel by default.
For example, in the fastest mode, with 1 µs settling time for the acquisition of each channel, a single analog
channel can be scanned continuously at 1 MS/s; two analog channels can be scanned at 500 kS/s each; 16
analog input channels can be scanned at 62.5 kS/s.
Settling time
For most applications, leave the settling time at its default of 1 µs.
However, if you are scanning multiple channels, and one or more channels are connected to a high-impedance
source, you may get better results by increasing the settling time. Remember that increasing the settling reduces
the maximum acquisition rate.
You can set the settling time to 1 µs, 5 µs, 10 µs, or 1 ms.
Example: Analog channel scanning of voltage inputs
Figure 4 shows a simple acquisition. The scan is programmed pre-acquisition and is made up of six analog
channels (Ch0, Ch1, Ch3, Ch4, Ch6, Ch7). Each of these analog channels can have a different gain. The
acquisition is triggered and the samples stream to the PC via DMA. Using the default settling time, each analog
channel requires one microsecond of scan time—therefore the scan period can be no shorter than 6 µs for this
example. The scan period can be made much longer than 6 µs—up to 1 second. The maximum scan frequency
is 1 divided by 6 µs, or 166,666 Hz.

Analog output

The PCI-2517 has four 16-bit, 1 MHz analog output channels.
The channels have an output range of -10V to +10V. Using Bus Mastering DMA, each D/A output can
continuously output a waveform at up to 1 MHz. In addition, a program can asynchronously output a value to
any of the D/A channels for non-waveform applications, if the D/A is not already being used in the waveform
output mode.
Figure 4. Analog channel scan of voltage inputs example
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Functional Details