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23 Chapter 3
When you set JP11 to EXT, the D/A converter takes its reference voltage
input from pin 31 of connector CN3. You can apply any voltage between
-10 V and +10 V to this pin to function as the external reference. The ref-
erence input can be either DC or AC (<100 kHz).
When you use an external reference with voltage V
ref
you can program
the D/A channel to output from 0 V to -V
ref
, you can also use the D/A
converter as a programmable attenuator. The attenuation factor between
reference input and analog output is:
Attenuation factor = G / 4095
G is a value you write to the D/A registers between 0 and 4095. For
example, if you set G to 2048, then the attenuation factor is 0.5. A sine
wave of 10 V amplitude applied to the reference input will generate a sine
wave of 5 V amplitude on the analog output.
3.2.4 Internal Voltage Reference, -10 V or -5 V (JP10)
If you use an internal reference voltage (set with JP11), the PCI-1718
cards provide a choice between -5 V or -10 V DC internal reference volt-
age sources.
Table 3-1: Summary of jumper JP10 settings
Table 3.4: Summary of Jumper JP10 Settings
Jumper Function description
JP10 5 V (default)
10 V