Chapter 4
Register Map and Descriptions
© National Instruments Corporation
4-31
AT-MIO-64F-5 User Manual
Analog Output Register Group
The two registers making up the Analog Output Register Group access the two analog output
channels. Data can be transferred to the DACs in one of three ways depending on the mode
configuration in Command Register 4 according to Table 4-6. Data can be directly sent to the
DACs from the local data bus, buffered from the local bus by the DAC FIFOs, or received
serially from the AT-DSP2200 across the RTSI bus. There are two methods of updating the
DACs, immediate and posted. In the immediate update mode, data transferred to the DACs is
not buffered, and is immediately converted to the appropriate voltage at the output. In the posted
update mode, data is converted to an output voltage only after a falling edge is detected on the
TMRTRIG* signal, or the DAC Update Register is strobed. In the immediate update mode and
the serial mode, the DAC FIFOs are not utilized. In all other output modes, the DAC FIFOs are
used.
The output voltage generated from the digital code depends on the configuration, unipolar or
bipolar, of the associated analog output channel. This configuration is determined by control bits
in the Command Register 2. Configuration bits in Command Register 2 determine if the digital
code written to the DACs is in straight binary form or in a twoÕs complement form. Table 4-10
shows the output voltage versus digital code for a unipolar analog output configuration.
Table 4-11 shows the voltage versus digital code for a bipolar analog output configuration.
The formula for the voltage output versus digital code for a unipolar analog output configuration
is as follows:
V
out
= V
ref
* (digital code)
4,096
where V
ref
is the reference voltage applied to the analog output channel. The digital code in the
above formula is a decimal value ranging from 0 to 4,095.
Table 4-10. Analog Output Voltage Versus Digital Code (Unipolar Mode)
Digital Code
Voltage Output
Decimal
Hex
V
ref =
10 V
0
0000
0 V
1
0001
2.44 mV
1,024
0400
2.5 V
2,048
0800
5 V
3,072
0C00
7.5 V
4,095
0FFF
9.9976 V
The formula for the voltage output versus digital code for a bipolar analog output configuration
in twoÕs complement form is as follows:
V
out
= V
ref
* (digital code)
2,048
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