Texas Instruments BUF16821EVM-USB, User Manual, Page: 20 / 33

BUF16821EVM-USB Software Overview
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20 SBOU106A – May 2011 – Revised May 2016
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BUF16821EVM-USB Evaluation Board and Software Tutorial
5.2.4 Write DAC Button
The method used to write the values in the DAC/V
COM
registers is based on whether or not the Auto Write
feature is enabled. The BUF16821 has two methods of writing information into the DAC/V
COM
registers.
The first method allows for the output voltage to change immediately after the writing to the DAC register.
In the BUF16821EVM-USB software, this mode is configured by enabling the Auto Write feature found in
the
Buffer dropdown menu. In this mode, as an individual channel is written to, the output voltage changes
as soon as the user moves to a different text box in the software. The second method of writing to the
DAC/V
COM
registers allows for the user to write multiple channels and then have all of the output voltages
change at the same time, rather than each channel voltage changing as soon as it is written to.
Disabling the Auto Write feature in the software allows the user to enter all of the values desired for all of
the channels and then press the
Write DAC button to change all of the output voltage of all of the
channels at one time. When the Auto Write feature is enabled, no change occurs to the output voltages
when the
Write DAC button is pressed. No change occurs because after the text box for a given channel
has been updated, as soon as another item in the software is clicked, the Auto Write feature automatically
performs a write command to the updated channel that then updates the output voltage. When in the Auto
Write enabled mode, the
Write DAC button cannot be pressed with different data in the corresponding
channel text boxes than the values already stored in the DAC/V
COM
register; thus, no change occurs.
Figure 18 shows the location in the Buffer Menu showing the Auto Write feature enabled. Clicking on the
Auto Write feature again enables/disables the feature, depending on its current state.
Figure 18. Auto Write Feature Enabled
5.2.5 Reset Button
Pressing the Reset button in the BUF16821EVM-USB software performs two functions. The first function
is to call a General-Call Reset for the BUF16821. The status of the DAC/V
COM
registers after this General-
Call Reset has been called depends upon whether the OTP has been programmed or not. If the OTP has
been programmed, the channel registers are loaded with the most recent values programmed into the
OTP memory. If the OTP memory has not been programmed, the channel registers default to
1000000000 , or mid-supply. The second function performed after the reset button is pressed is that a
Read DAC call is made to update the corresponding channel text boxes to the current value for each
channel.