MPR083 datasheet(33/56 Pages) FREESCALE

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Embedded Software Description

Blood Pressure Monitor Design Reference Manual, Rev. 0

Freescale Semiconductor

4-3

Initially, the MPR083 is configured to work with interrupts, so the IRQ output of the sensor can wake the

MCU when needed (using a KBI pin). After the configuration has been written the state machine enters an

idle state, during which it checks for a KBI interrupt, generated by a touch event in the sensor.

After a touch is detected, the state machine starts reading the FIFO register in the MPR083. Because the

FIFO register can store up to 30 touch-event values, it is read until it empties, and the last value is the one

used. The value of the electrode pressed is stored in a global variable and another variable is used to know

if the key was pressed or released.

The fault register in the sensor is used to determine if one or more electrodes were shorted to VDD or VSS.

After a fault is asserted, the sensor electrodes will no longer be scanned until the fault is cleared.

That is why after reading the FIFO register, the program reads the fault register, checking for errors. If no

error is detected, the state machine enters the idle state again. Otherwise, if a fault is detected, the state

machine goes to an error-clearing state. This is the procedure used to clear the fault:

1. Stop the electrode scanning by writing the configuration register (stop mode).

2. Clear the fault condition by writing the fault register.

3. Start the electrode scanning again by writing the configuration register (run mode).

After these steps are done, the state machine enters the idle state again, checking for any other electrode

touch event.

Configure

Idle

ReadFIFO

ReadFaul

ClearError

FIFO is not

empty yet

FIFO is empty

KBI interrupt

detected

Fault detected

No fault

detected

MPR083 Datasheet(PDF) 33 Page - Freescale Semiconductor, Inc