TDC1011_15 Datasheet, PDF (28/49 Pages) Texas Instruments – TDC1011 Single Channel Ultrasonic Sensing Analog Front End (AFE) for Level Sensing,Concentration Sensing Applications

TDC1011
SNAS662 – JULY 2015
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Device Function Description (continued)
8.4.6.5 TOF Measurement Interval
The comparators in the TDC1011's RX path can qualify and generate STOP pulses from a received echo within
an interval set by the TOF_TIMEOUT_CTRL field in the TIMEOUT register. The listening interval can be
extended in the standard TOF measurement (without blanking) by a period controlled with the TIMING_REG field
(see Standard TOF Measurement).
If the number of STOP events programmed in the NUM_RX field is not received within the listening interval, a
timeout event will occur and the device will return to the READY state. In addition, an error will be reported to the
ERROR_FLAGS register and the ERRB pin will be driven low.
The echo timeout can be disabled by setting the ECHO_TIMEOUT bit to 1 in the TIMEOUT register. If the echo
timeout is disabled, the device will not exit from the receive state until the expected number of STOP events set
in NUM_RX occur. If the number of events does not occur, the device can be forced out of the receive state by
writing a value of 0x03 to the ERROR_FLAGS register, or by de-asserting the EN pin, or asserting the RESET
pin.
NOTE
Writing a logic 1 to bit [1] of the ERROR_FLAGS register clears the state machine. Writing
a logic 1 to bit[0] clears the error flags.
NOTE
It is not recommended to hold the RX in an active state for intervals longer than 100ms, as
the comparator auto-zero may no longer be accurate.
8.4.7 Error Reporting
The TDC1011 will report an error when the receive signals do not match the expected configuration. The ERRB
pin will go low to indicate the presence of an error condition. Reading the ERROR_FLAGS register provides
information about the condition(s) that caused the error.
The ERR_SIG_WEAK bit indicates that the number of received and qualified zero-crossings was less than the
expected number set in the NUM_RX register field and a timeout occurred. This error is cleared when bit [0] is
written to 1.
The ERR_NO_SIG bit indicates that no signals were received and a timeout occurred. Writing a 1 to this bit
resets the state machine, halts active measurements and returns the device to SLEEP or READY mode. This
error is cleared when bit [0] is written to 1.
The ERR_SIG_HIGH bit indicates that the received echo amplitude exceeds the largest echo qualification
threshold at the input of the comparators. The ERR_SIG_HIGH error is only reported when the
ECHO_QUAL_THDL register field is set to 7h. Writing a 1 to this bit will reset all the error flags and reset the
ERRB pin to high.
NOTE
It is recommended to reset the state machine when the error flags are cleared. This can
be done simultaneously by writing a value of 0x03 to the ERROR_FLAGS register.
8.5 Programming
8.5.1 Serial Peripheral Interface (SPI)
The serial interface consists of serial data input (SDI), serial data output (SDO), serial interface clock (SCLK) and
chip select bar (CSB). The serial interface is used to configure the TDC1011 parameters available in various
configuration registers. All the registers are organized into individually addressable byte-long registers with a
unique address.
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