User`s guide

30 • Operation Theorem
4.1.6 A/D Data Format
The A/D data read from the FIFO is in the two‘s complement format. As
the A/D gain is 1, the A/D signal range is roughly +10V ~ -10V bi-polar. In
PCI-9111HR, the whole 16 bits A/D data are available. The relationship
between voltage and the A/D data value is shown in the following table:
A/D Data (Hex) Decimal Value Voltage (Volts)
7FFF +32767 +9.99969
4000 +16384 +5.00000
0001 1 +0.00031
0000 0 0.00000
FFFF -1 -0.00031
C000 -16384 -5.00000
8001 -32767 -9.99969
8000 -32768 -10.00031
Note: the decimal value of the A/D data is in the same sign with the
bi-polar voltage. Therefore, the sign extension conversion is not
necessary.
The A/D converted data of 12 bits PCI-9111DG is on the 12 MSBs of the
A/D data. The 4 LSB of the 16 bits A/D data are the channel number and
must be truncated by software. The relationship between voltage and the
A/D converted data value is shown in the following table:
A/D Converted
Data (Hex)
Decimal Value Voltage (Volts)
7FF +2047 +9.9951
400 +1024 +5.0000
001 +1 +0.0049
000 0 0.0000
FFF -1 -0.0049
C00 -1024 -5.0000
801 -2047 -9.9951
800 -2048 -10.0000
The formula between the A/D converted data and the voltage value is:
Voltage AD data
K gain
= × ×_
1 10
where gain is the value of the A/D gain control register. K=32768 for
PCI-9111HR, and K=2048 for PCI-9111DG.