MPR121 datasheet(46/57 Pages) FREESCALE

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MPR121

Sensors

Freescale Semiconductor

PWM0[3:0] ~ PWM7[3:0] is used to set the PWM duty of GPIO0 ~ GPIO7 respectively. The power up reset default setting for

these four register is 0x00. When a GPIO is programmed as output and the DAT register is “1” and if the corresponding PWM_

[3:0] register is not zero, the GPIO pin outputs PWM waveform. The PWM period is fixed 8ms (1/256 of 32 KHz OSC) and PWM_

[3:0] register decides duty of the waveform.

These register can be read/write any time, even if MPR121 is in Run Mode. When the register changes during PWM enables,

a mixed duty cycle would be possible to occur.

The PWM duty is not so much accurate, because GPIO output transition (include PWM) inhibits during measurement state.

Therefore, when interval time (=Touch Detection Sample Interval) is close to measurement time (depends on charge time, AFE

Samples and number of measurement electrodes), the PWM operation is disturbed and the waveform couldn’t keep programmed

duty.

PWM_ [3:0]

Description (_ is 0~7)

PWM is off, GPIO outputs stable high when DAT register is “1”

GPIO output duty is 1:15 (mostly output low)

GPIO output duty is 2:14 (mostly output low)

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GPIO output duty is 15:1 (mostly output high)

MPR121 数据表(PDF) 46 Page - Freescale Semiconductor, Inc