The effect of this interpolation at the system level is a 50% reduction in sample jitter. Figure 24 shows the resulting output data
for an input signal.
80
75
Internally
Sampled Values
70
65
60
55
Earliest Transmission
Point of Interpolated
Values
Earliest Transmission
Fixed Latency:
t S / 2
Point of Internally
Sampled Values
50
45
40
Window of
Transmission for
Interpolated Values
(Maximum: t S / 2)
Window of
Transmission for
= Signal Jitter = Sampled Values
(Maximum: t S / 2)
0
5
10
15
20
25
30
35
40
Input Signal
Time
Internally Sampled Signal
Interpolated Samples
Figure 24. Data Interpolation Example
3.8.9
Acceleration Data Timing
The SPI uses a request/response protocol, where a SPI transfer is completed through a sequence of 2 phases. Reference
Section 4 for more details regarding the SPI protocol. The device latches the associated data for an acceleration request at the
rising edge of CS. The most recent sample available from the DSP (including interpolation) is latched, and transmitted during the
subsequent SPI transfer.
SCLK
CS
MOSI
Request X-Axis
Request Y-Axis
X-Axis Response
Request X-Axis
Y-Axis Response
Request Y-Axis
X-Axis Response
MISO
X-Axis Data Latched
X-Axis Arm Function updated
Y-Axis Data Latched
Y-Axis Arm Function updated if applicable
Figure 25. Acceleration Data Timing
MMA65xx
Sensor
36
Freescale Semiconductor, Inc.
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