MC3630 Datasheet, PDF (54/83 Pages) –

MC3630 3-Axis Accelerometer
Preliminary Datasheet
(0x13) Sniff Threshold Control Register
This register sets the threshold values used by the SNIFF logic for activity detection. For each
axis, a delta count is generated and compared to the threshold. When the delta count is
greater than the threshold, a SNIFF wakeup event occurs. There is a unique sniff threshold for
each axis, and an optional “false detection count” which requires multiple sniff detection events
to occur before a wakeup condition is declared. These features are set by six shadow registers
accessed by register 0x13[5:0] and register 0x14 bits [2:0]. Usage of sniff block is described in
application note AN-003.
The SNIFF block supports the logical AND or OR of the X/Y/Z SNIFF wakeup flags when
generating a SNIFF wakeup interrupt.
The SNIFF block supports two methods of calculating SNIFF delta counts:
 Current Sample to Previous Sample (C2P)
o The current sample and the immediate previous sample are subtracted to
generate a delta
 Current Sample to Baseline (C2B)
o The current sample and the first sample captured when entering SNIFF mode
are subtracted to generate a delta.
Bit
POR
Addr Name
7
6
5
4
3
2
1
0
Value R/W
0x13 SNIFFTH SNIFF_ SNIFF_ SNIFF_TH SNIFF_TH SNIFF_TH SNIFF_TH SNIFF_TH SNIFF_TH 0000000 WS
_C
MODE AND_OR
[5]
[4]
[3]
[2]
[1]
[0]
0
Bit
[5:0]
Name
SNIFF_TH[5:0]
Description
This 6-bit field accesses six shadow registers behind
address 0x13. Register 0x14 bits [2:0] control which register
is accessed.
Reg 0x14
SNIFF_T_ADDR[2:0]
Reg 0x13
SNIFF_TH[5:0]
000
None
001
SNIFF Threshold, X-axis
SNIFF_TH_X[5:0], unsigned
threshold value 0 to 63 (independent
from Y and Z thresholds).
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