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Note
If only one transition from a state is used, STx_TCONFA and STx_TCONFB should be
configured equally.
To prevent unnecessary interrupt requests or PRS outputs when the decoder toggles back and forth
between two states, a hysteresis option is available. The hysteresis function is triggered if a type A
transition is preceded by a type B transition, and vice versa. A type A transition is a transition defined in
STx_TCONFA, and a type B transition is a transition defined in STx_TCONFB. When descriptor chaining
is used, a jump to another descriptor will cancel out the hysteresis effect. Figure 25.8 (p. 624) illustrates
how the hysteresis triggers upon state transitions.
Figure 25.8. Decoder hysteresis
St at e 0
1: B transition, no hysteresis
A t ransit ion: Transit ion defined in TCONFA
B t ransit ion: Transit ion defined in TCONFB
St at e 1
2: A transition, hysteresis
3: B transition, hysteresis
St at e 2
4: A transition, hysteresis
5: A transition, no hysteresis
St at e 3
The events suppressed by the hysteresis are configured in bit fields HYSTPRS0-2 and HYSTIRQ in
DECCTRL.
• When HYSTPRSx is set, PRS signal x is suppressed when the hysteresis triggers.
• When HYSTIRQ is set, interrupt requests are suppressed when the hysteresis triggers.
Note
The decoder error interrupt flag, DECERR, is not affected by the hysteresis.
25.3.7 Measurement results
Part of the LESENSE RAM is treated as a circular buffer for storage of up to 16 results from sensor
measurements. Each time LESENSE writes data to the result buffer, the result write pointer, PTR_WR,
is incremented. Each time a new result is read through the BUFDATA register, the result read pointer,
PTR_RD, is incremented. The read pointer will not be incremented if there is no valid, unread data in
the result buffer. By default LESENSE will not write additional data to a full result buffer until the data is
read by software or DMA. Setting BUFOW in CTRL enables LESENSE to write to the result buffer, even
if it is full. In this mode, the result read pointer will follow the write pointer if the buffer is full. The result of
this is that data read from the result read register, BUFDATA, is the oldest unread result. The location
pointers are available in PTR. The result buffer has three status flags; BUFDATAV, BUFHALFFULL,
and BUFFULL. The flags indicate when new data is available, when the buffer is half full, and when it is
full, respectively. The interrupt flag BUFDATAV is set when data is available in the buffer. BUFLEVEL
is set when the buffer is either full or half-full, depending on the configuration of BUFIDL in CTRL. If the
result buffer overflows, the BUFOF interrupt flag will be set.
During a scan, the state of each sensor is stored in SCANRES. If a sensor triggers, a 1 is stored in
SCANRES, else a 0 is stored in SCANRES. Whether or not a sensor is said to be triggered depends of
the configuration for the given channel. If SAMPLE is set to ACMP, the sensor is said to be triggered
if the output from the analog comparator is 1 when sensor sampling is performed. If SAMPLE is set to
COUNTER, a sensor is said to be triggered if the LESENSE counter value is greater than or equal, or
2013-05-08 - Wonder Gecko Family - d0233_Rev0.50
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