ADC 6015 Specifiche Scaricare il pdf (Pagina 6)

dsPIC30F6010A/6015

7. Module: QEI Interrupt Generation

The Quadrature Encoder Interface (QEI) module

does not generate an interrupt when MAXCNT is

set to 0xFFFF and the following events occur:

1. POSCNT underflows from 0x0000 to 0xFFFF.

2. POSCNT stops.

3. POSCNT overflows from 0xFFFF to 0x0000.

This sequence of events occurs when the motor is

running in one direction, which causes POSCNT to

underflow to 0xFFFF. Once this happens, the

motor stops and starts to run in the opposite

direction, which generates an overflow from

0xFFFF to 0x0000. The QEI module does not

generate an interrupt when this condition occurs.

Work around

To prevent this condition from occurring, set

MAXCNT to 0x7FFF, which will cause an interrupt

to be generated by the QEI module.

In addition, a global variable could be used to keep

track of bit 15, so that when an overflow or

underflow condition is present on POSCNT, the

variable will toggle bit 15. Example 1 shows the

code required for this global variable.

EXAMPLE 1:

unsigned int POSCNT_b15 = 0;

unsigned int Motor_Position = 0;

int main(void)

{

// ... User's code

MAXCNT = 0x7FFF; // Instead of 0xFFFF

Motor_Position = POSCNT_b15 + POSCNT;

// ... User's code

}

void __attribute__((__interrupt__)) _QEIInterrupt(void)

{

IFSxbits.QEIIF = 0; // Clear QEI interrupt flag

// x=2 for dsPIC30F

// x=3 for dsPIC33F

POSCNT_b15 ^= 0x8000; // Overflow or Underflow

}

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ADC 6015 Specifiche Pagina 6