Datasheet
MMA8451Q
Sensors
42 Freescale Semiconductor, Inc.
6.8 Control Registers
Note: Except for STANDBY mode selection, the device must be in STANDBY mode to change any of the fields within
CTRL_REG1 (0x2A).
0x2A: CTRL_REG1 System Control 1 Register
It is important to note that when the device is Auto-SLEEP mode, the system ODR and the data rate for all the system
functional blocks are overridden by the data rate set by the ASLP_RATE field.
DR[2:0] bits select the Output Data Rate (ODR) for acceleration samples. The default value is 000 for a data rate of 800 Hz.
ACTIVE bit selects between STANDBY mode and ACTIVE mode. The default value is 0 for STANDBY mode.
LNOISE bit selects between normal full dynamic range mode and a high sensitivity, Low Noise mode. In Low Noise mode, the
maximum signal that can be measured is ±4g. Note: Any thresholds set above 4g will not be reached.
F_READ bit selects between normal and Fast Read mode. When selected, the auto increment counter will skip over the LSB
data bytes. Data read from the FIFO will skip over the LSB data, reducing the acquisition time. Note F_READ can only be
changed when FMODE = 00. The F_READ bit applies for both the output registers and the FIFO.
0x2A: CTRL_REG1 Register (Read/Write)
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
ASLP_RATE1 ASLP_RATE0 DR2 DR1 DR0 LNOISE F_READ ACTIVE
Table 61. CTRL_REG1 Description
ASLP_RATE[1:0]
Configures the Auto-WAKE sample frequency when the device is in SLEEP Mode. Default value: 00.
See Table 62 for more information.
DR[2:0]
Data rate selection. Default value: 000.
See Table 63 for more information.
LNOISE
Reduced noise reduced Maximum range mode. Default value: 0.
(0: Normal mode; 1: Reduced Noise mode)
F_READ
Fast Read mode: Data format limited to single Byte Default value: 0.
(0: Normal mode 1: Fast Read Mode)
ACTIVE
Full Scale selection. Default value: 00.
(0: STANDBY mode; 1: ACTIVE mode)
Table 62. SLEEP Mode Rate Description
ASLP_RATE1 ASLP_RATE0 Frequency (Hz)
00 50
0 1 12.5
1 0 6.25
1 1 1.56
Table 63. System Output Data Rate Selection
DR2 DR1 DR0 ODR Period
0 0 0 800 Hz 1.25 ms
0 0 1 400 Hz 2.5 ms
0 1 0 200 Hz 5 ms
0 1 1 100 Hz 10 ms
1 0 0 50 Hz 20 ms
1 0 1 12.5 Hz 80 ms
1 1 0 6.25 Hz 160 ms
1 1 1 1.56 Hz 640 ms
Table 64. Full Scale Selection
Active Mode
0STANDBY
1ACTIVE