Sensors

Freescale Semiconductor

15

MMA7455L

ASSIGNING, CLEARING & DETECTING INTERRUPTS

Assigning the interrupt pins is done in Register $18. There are 3 combinations for the interrupt pins to be assigned which are

outlined below in the table for INTREG[1:0].

Table 7. Configuring the Interrupt settings using Register $18 with INTREG[1:0] bits

00: INT1 Register is detecting Level while INT2 is detecting Pulse.

01: INT1 Register is detecting Pulse while INT2 is detecting Level.

time window and second time window > 0 then INT2 will detect the double pulse only.

INTPIN: INT1 pin is routed to INT1 bit in Detection Source Register ($0A) and INT2 pin is routed to INT2 bit in Detection Source

Register ($0A).

INTPIN: INT2 pin is routed to INT1 bit in Detection Source Register ($0A) and INT1 pin is routed to INT2 bit in Detection Source

Register ($0A).

Note: When INTREG[1:0] =10 for the condition to detect single pulse on INT1 and either single or double pulse on INT2, INT1

register bit can no longer be cleared by setting CLR_INT1 bit. It is cleared by setting CLR_INT2 bit. In this case, setting CLR_INT2

clears both INT1 and INT2 register bits and resets the detection operation. Follow the example given for clearing the interrupts.

Clearing the Interrupt Pins: Register $17

CLR_INT1

1: Clear “INT1”

0: Do not clear “INT1”

CLR_INT2

1: Clear “INT2”

0: Do not clear “INT2”

After interrupt has triggered due to a detection, the interrupt pin (INT1 or INT2) need to be cleared by writing a logic 1. Then the

interrupt pin should be enabled to trigger the next detection by setting it to a logic 0.

This example is to show how to reset the interrupt flags

void ClearIntLatch(void)

{

IIC_ByteWrite(INTRST, 0x03);

IIC_ByteWrite(INTRST, 0x00);

}

$18 Control 1 Register

D7

D6

D5

D4

D3

D2

D1

D0

Reg $18

DFBW

THOPT

ZDA

YDA

XDA

INTREG[1]

INTREG[0]

INTPIN

Function

000000

00

Default

INTREG[1:0]

“INT1” Register Bit

“INT2” Register Bit

00

Level detection

Pulse Detection

01

Pulse Detection

Level Detection

10

Single Pulse detection

Single or Double Pulse Detection

$17: Interrupt Latch Reset (Read/Write)

D7

D6

D5

D4

D3

D2

D1

D0

Reg $17

--

--

--

--

--

--

CLR_INT2

CLR_INT1

Function

000000

00

Default