Immediate DAC Update Mode

Digital-to-Analog Converter Board Programming Options

There are two types of registers that must be written to for proper operation of the DAC board. One is the CSR, and the other is the DAC. The order in which they are written to may differ depending on the method used to start a conversion.

The IMMEDIATE DAC UPDATE MODE is described in “Program Control Update Mode” on page 4-4 and the board is configured for this mode when received from the factory. Once this has been set up, a 16-bit word can be written to any DAC channel where it will begin immediate analog conversion. When byte transfer (8-bit) is used to load the DAC channel, conversion begins immediately upon the loading of the high byte (D15 to D8).

All eight DAC channels can be initiated to a value, as described in the preceding paragraph, before they are connected to the external circuitry. After powering up the board, load the DAC channels with the initial 16-bit word (or two 8-bit bytes) required (positive true offset binary or binary two's complement coding, Table 3-3 below). A control word can then be written to the CSR to enable the DAC outputs to the P3 connector. The CSR bit description for this mode of operation is detailed in Table 3-4 on page 3-4 and Table 3-5 on page 3-5.

Table 3-3. DAC Data Format Analog Output versus Digital Input (±10 V Scale)

Digital Input Code

Offset Binary Coding

Analog Output Voltage	Two’s Complement

(MSB)

D15

0000

0100

1000

1100

1111

0000

1111

0000

1111

(LSB)

0000

0001

0000

1111

-10.000V

-5.000V

0.000V

305μV

+5.000V

9.99969V

-Full Scale

-1/2 Scale

Zero

+LSB

+1/2 Scale

+Full Scale

1000

1100

0000

0100

0111

0000

1111

0000

1111

0000

0001

0000

1111

The analog output may be calculated by the input code written by the processor to the selected

DAC channel as follows:

Analog Output = -10 V + ([(Digital Input Code in decimal) X 20]/65536)

GFK-2059

Chapter 3 Programming

3-3