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GFK-2059 Chapter 3 Programming 3-3
3
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.
Immediate DAC Update Mode
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)
Offset Binary Coding
Digital Input Code
(MSB)
D15
(LSB)
D0
Analog Output Voltage Two’s Complement
0000 0000 0000 0000 -10.000V -Full Scale 1000 0000 0000 0000
0100 0000 0000 0000 -5.000V -1/2 Scale 1100 0000 0000 0000
1000 0000 0000 0000 0.000V Zero 0000 0000 0000 0000
1000 0000 0000 0001
305µV
+LSB 0000 0000 0000 0001
1100 0000 0000 0000 +5.000V +1/2 Scale 0100 0000 0000 0000
1111 1111 1111 1111 9.99969V +Full Scale 0111 1111 1111 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)