User`s guide

Operation Theory • 43

4.1.7 A/D Data Format

The A/D data read from the FIFO is in two’s complement format. As the A/D

gain is 1, the A/D signal range is roughly +10V ~ -10V bi-polar. In the

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

Table 2: Relationship between voltage and A/D data value

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 the 12-bit PCI-9111DG is on the 12 MSB of the A/D

data. The 4 LSB of the 16 bits A/D data are the channel number and must be

truncated by the 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

Table 3: Relationship between voltage and A/D converted data