Chapter 4 Register Map and Descriptions
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National Instruments Corporation 4-41 AT-MIO-16X 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 bu ff ered ,
and is immediately converted to the appropriate voltage a t the outpu t.
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 DA C
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 two’s 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:
Vout = Vref * (digital code)
65,536
where Vref is the reference voltage applied to the analog output channel.
The digital code in the above formula is a decimal value r anging fr om
0 to 65,535.