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EVM Software Overview
13
SBAU248 – November 2016
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Copyright © 2016, Texas Instruments Incorporated
DAC8775EVM User’s Guide
4.3
Device Controls
This section describes the GUI controls for the internal reference, power-on conditions, clear, software
reset, and DAC broadcast functionality.
4.3.1
Internal Reference
The internal reference can be enabled or disabled using the internal reference control on the EVM GUI. By
default, the internal reference is disabled.
4.3.2
Power-On Condition
By default the power-on state of the current output is Hi-Z and the voltage output is 30 k
Ω
to ground after
a clear or reset command. The power-on condition GUI control allows control of the voltage output power-
on condition as either 30 k
Ω
to ground or Hi-Z.
4.3.3
Software Reset
The RESET button on the GUI issues a software reset to the DAC8775, restoring the default power-on
register contents. The GUI immediately reads all of the registers of the device to synchronize the GUI and
hardware. A hardware reset can be issued through JP14. If a hardware issue is issued the READ ALL
button should be pressed to synchronize the GUI and hardware.
4.3.4
Software Clear
The CLEAR button on the GUI issues a clear command to the DAC8775, restoring the DAC data registers
to full-scale or zero-scale based on each channel’s clear select settings and clear enable settings. After a
clear command is issued the GUI immediately reads the data registers of the device to synchronize the
GUI and hardware. A hardware clear command can be issued through JP12. If a hardware clear is issued
the READ ALL button should be pressed to synchronize the GUI and hardware.
4.4
DAC Controls
4.4.1
DAC Outputs
The DACs can be configured for voltage or current outputs of various spans through the Output Mode
control on the GUI. The DAC output can be set to active or inactive by checking or removing the check
from the Output Enable Boolean control on the GUI. Once an output range is selected and the output is
enabled, the DAC output value can be controlled by writing values to the DAC Data control. The DAC
Data control expects hexadecimal input formats. The small indicator on the left side of the DAC Data
control can be used to change the input data format.
Output current drive can be programmatically limited for each of the voltage output modes through the
V
OUT
Current Limit control on the GUI. Take note that the actual current limit will be compliant to the values
specified in the DAC8775 electrical characteristics table.
4.4.2
Clear Functionality
Each DAC output has a Clear Enable Boolean that is AND’d with the CLEAR command. If the Clear
Enable Boolean is checked, the output channel will respond to a clear event; conversely, if the Boolean is
unchecked, the output channel will not respond to a clear event. Each DAC can be programmed to clear
to either zero-scale or full-scale. This behavior can be controlled by the Clear Select control on the GUI.
4.4.3
HART Inputs
The enable HART signals to be coupled to the current outputs through the onboard coupling path the
HART-Enable Boolean control must be checked.