Data Sheet - Freescale Semiconductor
Data Sheet - Freescale Semiconductor
Data Sheet - Freescale Semiconductor
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Figure 26. 0.1 Hz offset cancellation low-pass filter characteristics<br />
3.5.4.6 Offset monitor<br />
The device includes an offset monitor circuit. The offset monitor is enabled 2.1 seconds following reset regardless of the state of<br />
the OC_FILT bits in the ACC_CFG register. The output of the single pole, low-pass filter in the offset cancellation block is<br />
continuously monitored against the offset limits specified in Section 2.4. An up/down counter is employed to count up If the output<br />
exceeds the limits, and to count down if the output is within the limits. The output of the counter is compared against the count<br />
limit OFFMONCNTLIMIT . If the counter exceeds the limit, the OFFSET_ERR bit in the ACC_STAT register and in the DEVSTAT<br />
register is set. The counter rails once the max counter value is reached (OFFMONCNTSIZE). 3.5.4.7 <strong>Data</strong> interpolation<br />
The device includes 16 to 1 linear data interpolation to minimize the system sample jitter. Each result produced by the digital<br />
signal processing chain is delayed one sample time. On detection of a Periodic <strong>Data</strong> Collection Mode command, the transmitted<br />
data is interpolated from the one previous samples, resulting in a latency of one sample time, and a maximum signal jitter of 1 μs.<br />
3.5.4.8 Output scaling<br />
The 26-bit digital output from the DSP is clipped and scaled to a 10-bit, 14-bit, or 16-bit data word. The 10-bit and 14-bit data<br />
words are used for Periodic <strong>Data</strong> Collection Mode and the 16-bit range is stored in the ACC_DATAH and ACC_DATAL registers<br />
for access during Command and Response Mode.<br />
The sensitivity of the data is the same for all ranges. If the 14-bit data length is selected, four additional bits of range are<br />
transmitted. If the ACC_DATAH and ACC_DATAL registers are accessed, six additional bits of range are available. These<br />
additional bits of range are intended for test use only and are not covered by the specifications listed in Section 2.4. Reference<br />
Table 37 for the acceleration data values for all ranges.<br />
MMA27XXW<br />
Sensors<br />
<strong>Freescale</strong> <strong>Semiconductor</strong>, Inc. 53
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