ADLINK PXI-2502 - Manual (Page 35)

Operation Theorem
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Setting up the DACs
Before using the DACs, users should setup the reference source and its
polarity. Each DAC has its own reference and polarity settings. For ex-
ample; the internal voltage reference of D/A Group A is tied to internal
+10V, however, users can still connect external reference thru AOEXTREF
(pin 5 on CN2), for example to a +3.3V voltage source. Therefore, each
DAC in D/A Group A has two reference options: 10V or 3.3V. However, DA
update timing, trigger Source, and trigger/stop mode are all the same
throughout that D/A Group.
DAQ/PXI-2500 SERIES provides the capability to fine tune the voltage
reference from the external source. The external reference is fed thru an
on board calibrated circuit, with programmable offset. Users can utilize this
capability to generate precise D/A outputs.
CAUTION: The range of external voltage reference should be within
10V.
Utilizing Multiplying Characteristic of DACs
The D/A reference selection let users fully utilize the multiplying charac-
teristics of the DACs. Digital codes sent to the D/A converters will be
multiplied by the reference to generate output.
Bipolar Unipolar
Magnitude
Output Output
Digital
Code
FSR – LSB
+Vref * (2046 /
2048)
Vref * (4095 / 4096) 0FFF
Midscale +
LSB
+Vref * (1 / 2048) Vref * (2049 4096) 0801
Midscale 0 Vref * (2048 / 4096) 0800
Midscale –
LSB
-Vref * ( 1 / 2048) Vref * (2047 / 4096) 07FF
-FSR + LSB
-Vref * (2046 /
2048)
Vref * ( 1 / 4096) 0001
-FSR -Vref 0 0000
Table 4.2.1 D/A Output Versus Digital Codes