MMA8451Q Int not clearing

scottbuchanan — Tue, 03 Feb 2026 23:06:27 GMT

Description: I'm using one of your MMA8451 3axis devices with a Nordic

Semi nrf51822. I'm using the built-in function to detect a tap and

a flip. The tap is directed to INT1 and the flip is directed to INT2.

I can currently detect both interrupts and distinguish between

them based on which GPIO pin on the nrf51822 is driven. The

GPIO pins are configured as pull-up's.

I've been using int1 and the tap detection for a while with no

problem. I added the flip detection to INT2 today and now,

occasionally, after the int serv. routine is triggered one, or the

other (depending on which was triggered) will not reset after

reading the appropriate status register. I do read both status

registers each time to be safe - PL_STATUS_REG and

PULSE_SRC_REG - and the values look correct.

I'm measuring the INT pin voltages and once this occurs either

INT1 or INT2 stays low and no more interrupts are generated by

the accel until a power cycle.

Can you help with some suggestions as to what I'm doing

wrong?

The init routing to set up the accel is in the attached file after the

pre-processor.

void accel_init(void)

{

uint8_t regValue, newRegValue;

turn_off_accel();

newRegValue = 0x10;

regValue = twi_read_register(0x3A, 0x2A);

twi_write_register(0x3A, 0x2A, (regValue & 0xC7) | 0x10);

twi_write_register(0x3A, 0x21, (0x00 | 0 << 6 | 0 << 5 | 1 << 4 | 0 << 3 | 1 << 2 | 0 << 1 | 1 << 0));

uint8_t ac = ((uint8_t)((double)1.575/0.063));

twi_write_register(0x3A, 0x23, ((uint8_t)((double)1.575/0.063)));

twi_write_register(0x3A, 0x24, ((uint8_t)((double)1.575/0.063)));

twi_write_register(0x3A, 0x25, ((uint8_t)((double)2.65/0.063)));

twi_write_register(0x3A, 0x26, ((uint8_t)(50 / 2.5)));

twi_write_register(0x3A,0x27, ((uint8_t)(140 / 5.0)));

twi_write_register(0x3A, 0x2A, 0x10 | 0 << 2);

twi_write_register(0x3A, 0x2B, (0x00 | 1 << 0 | 1 << 3 | 1 << 1 | 1 << 4 | 0 << 2));

twi_write_register(0x3A, 0x2C, 0x00);

twi_write_register(0x3A, 0x2D, (0x00 | 0 << 2 | 1 << 3 | 1 << 4));

twi_write_register(0x3A, 0x2E, (0x00 | 0 << 2 | 1 << 3 | 0 << 4));

twi_write_register(0x3A, 0x11, 0x40);

twi_write_register(0x3A, 0x13, 0xC0);

twi_write_register(0x3A, 0x14, (0x07 << 3 | 0x01));

twi_write_register(0x3A, 0x12, ((uint8_t)(100 / 5.0)));

topic MMA8451Q Int not clearing in Sensors