Texas Instruments XTR108, User Manual

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60 SBOU123A – March 2012 – Revised September 2016
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The USB-DAQ Platform SPI protocol supports four clock and data line modes of operation. These modes
are summarized in
Table 32 . The first mode, BREH, is used by the XTR108EVM-USB.
Table 32. SPI Modes of Operation
Mode Clock Polarity Description (CPOL) Clock Transition for Data Polarity Description (CPHA)
BREH
Clock idles low
CPOL = 0
Data are read by the USB-DAQ on the clock rising edge. Data are
changed by the USB-DAQ on the clock falling edge. Data are sampled on
the first clock edge. CPHA = 0.
BREL
Clock idles low
CPOL = 0
Data are read by the USB-DAQ on the clock falling edge. Data are
changed by the USB-DAQ on the clock rising edge. Data are sampled on
the second clock edge. CPHA = 1.
AFEH
Clock idles high
CPOL = 1
Data are read by the USB-DAQ on the clock falling edge. Data are
changed by the USB-DAQ on the clock rising edge. Data are sampled on
the first clock edge. CPHA = 0.
AFEL
Clock idles high
CPOL = 1
Data are read by the USB-DAQ on the clock rising edge. Data are
changed by the USB-DAQ on the clock falling edge. Data are sampled on
the second clock edge. CPHA = 1.
The USB-DAQ also supports a set of generic commands used to enable or disable power supplies, read
from internal ADCs, set the output of internal DACs, and set the voltage of control pins. The XTR108EVM-
USB uses the GPIO pin functionality to control the relay driver U1 on the Interface Board. These
commands are given in
Table 33 .
Table 33. General USB-DAQ Commands
Command Description
CMD Always the first mnemonic in a general USB-DAQ command.
Example: CTRL 0, CTRL 3, CTRL 128,
CTRL 255
Sets the eight control pins according to the value written.
Each control pin is assigned a location in the 8-bit control word, where CTRL8 is the
MSB and CTRL1 is the LSB. For example, write CTRL 0 to turn off all control pins. To
turn on the CTRL1 and CTRL2 pins, write CTRL 3. To turn on only the CTRL8 pin,
write CTRL 128.
Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (March, 2012) to A Revision ...................................................................................................... Page
• Deleted all references to included power supply. A power supply is no longer included with this EVM.
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