Analog Output Circuitry; Figure 4-4. Analog Output Circuitry Block Diagram - National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual

Chapter 4

Analog Output Circuitry

The Lab-PC+ provides two channels of 12-bit D/A output. Each analog output channel can
provide unipolar or bipolar output. Figure 4-4 shows a block diagram of the analog output
circuitry.
DAC0WR
Data
8
DAC1WR
Counter
A2
CNFGWR
Each analog output channel contains a 12-bit DAC. The DAC in each analog output channel
generates a voltage proportional to the input V
DAC. Each DAC can be loaded with a 12-bit digital code by writing to the DAC0 (L and H) and
DAC1 (L and H) Registers on the Lab-PC+ board. The voltage output from the two DACs is
available at the Lab-PC+ I/O connector DAC0 OUT and DAC1 OUT pins.
The DAC voltages can be updated in any of three ways, depending on the setting of the LDAC
bit. If this bit is cleared, the DAC output voltage is updated as soon as the corresponding DAC
Data Register is written to. If the LDAC bit is set, the DAC output voltage does not change until
a falling edge is detected either from Counter A2 or from EXTUPDATE*.
© National Instruments Corporation
2SDAC0
Coding
Ref
Ref
Coding
2SDAC1
Command Register 2
2SDAC1
LDAC1

Figure 4-4. Analog Output Circuitry Block Diagram

DAC0
5 V Internal
Reference
DAC1
2SDAC0
LDAC0
multiplied by the digital code loaded into the
ref
4-9
Theory of Operation
DAC0 OUT
AGND
DAC1 OUT
EXTUPDATE*
Lab-PC+ User Manual