ADIS16201 Analog Devices, Inc., ADIS16201 Datasheet - Page 17

• Manufacturer Part Number: ADIS16201
• Description: Programmable Dual-axis Inclinometer/accelerometer
• Manufacturer: Analog Devices, Inc.

PROGRAMMING AND CONTROL
CONTROL REGISTER OVERVIEW
The ADIS16201 offers many programmable features that are
controlled by writing commands to the appropriate control
registers using the SPI. For added system flexibility and
programmability, the following sections describe these controls
and specify the 28 digital control registers that are available
using the SPI interface. A high level listing of these registers is
given within Table 9. The following sections expand upon the
functionality of each of these control registers, providing for the
full clarification of the behavior of each of the control registers.
Available control modes for the device include selectable sample
rates for reading the seven output vectors, configurable output
data, alarm settings, control of the on-board 12-bit auxiliary
DAC, handling of the two general-purpose I/O lines, facilitation
of the sleep mode, enabling the self-test mode, and other
miscellaneous control functions.
The conversion process is repeated continually, providing for
continuous update of the seven output registers. The new data
ready bit (ND) flags bits common to all seven output registers,
allowing the completion of the conversion process to be tracked
via the SPI. As an alternative, the digital I/O lines can be configured
through software control to create a data-ready hardware function
that can signal the completion of the conversion process.
Two independent alarms provide the ability to monitor any one
of the seven output registers. They can be configured to report
an alarm condition on either fixed thresholds or rates of change.
The alarm conditions are monitored through the SPI. In addition,
the user can configure the digital I/O lines through software
control to create an alarm function that allows for monitoring
of the alarm conditions through hardware.
The seven output signals noted above are calibrated independ-
ently at the factory, delivering a high degree of accuracy. In
addition, the user has access to independent offset and scale
factors for each of the two acceleration and inclination output
vectors. This allows independent scaling and level adjustment
control of any one these four registers prior to the values being
read via the SPI. In turn, field level calibrations can be implemented
within the sensor itself using these offset and scale variables.
System level commands provided within the sensor include
automatic zeroing of the four outputs using a single null command
via the SPI. In addition, the original factory calibration settings
can be recovered at any point, using a simple factory reset
command.
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CONTROL REGISTER ACCESS
The control registers within the ADIS16201 are based upon a
16-bit/2-byte format, and they are accessed via the SPI. The SPI
operates in full duplex mode with the data clocked out of the
DOUT pin at the same time data is clocked in through the DIN
pin. All commands written to the ASIS16201 are categorized as
write commands or read commands. All write commands are
self-contained and take place within a single cycle. Each read
command requires two cycles to complete; the first cycle is for
transmitting the register address, and the second cycle is for
reading the data. During the second cycle, when the data out
line is active, the data in line is used to receive the next
sequential command. This allows for overlapping the commands.
For more information on basic SPI port operation, see the
Applications section.
The read and write commands are identified through the most
significant bit (MSB), B15, of the received data. Write a 1 to B15
to indicate a write command. Write a 0 to B15 to indicate a read
command. Bit B13 through Bit B8 contain the address of the
control register that is being accessed. The remaining eight bits of
the write command contain the data that is being written into the
part, whereas the remaining eight bits of the read command
contain don’t care levels. Given that the data within the write
command is eight bits in length, the 8-bit data format is the
default byte size. A write command operates on a single chip
select cycle, as shown in Figure 35. The read command operates
on a 2-chip select cycle basis, as seen in Figure 34. All 64 bytes of
register space are accessed using the 6-bit address. Data written
into the device is one byte at a time with the address of each byte
being explicitly called out in the write command. Conversely, data
being read from the device consists of two, back-to-back, 8-bit
variables being sent out, with the first byte out corresponding to
the upper address (odd number address) and the second byte
relating to the next lower address space (even number address).
For example, a data read of Address 03h results in the data from
Address 03h being fed out followed by data from Address 02h.
Likewise, a data read of Address 02h results in the same data
stream being output from the device.
The ADIS16201 is a flash-based device with the nonvolatile
functional registers implemented as flash registers. Take into
account the endurance limitation of 20,000 writes when
considering the system-level integration of these devices. The
nonvolatile column in Table 9 indicates which registers are
recovered upon power-up. The user must instigate a manual
flash update command (using the command register) in order
to store the nonvolatile data registers, once they are configured
properly. When performing a manual flash update command,
the user needs to ensure that the power supply remains within
limits for a minimum of 50 μs after the write is initiated. This
ensures a successful write of the nonvolatile data.
ADIS16201