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USING THE ST7 SPI TO EMULATE A 16-BIT SLAVE

Figure 2. Data Register Block diagram

2 SOFTWARE

Figure 3. C code (COSMIC C Compiler) for the interrupt routine

DATA REGISTER

INTERNAL BUS

MISO

MOSI

READ REGISTER

8-BIT

SHIFT REGISTER

@interrupt @nostack void SPI_Interrupt(void)

{

volatile TwoBytes twobytesDR;

if (ValBit(SPISR,SPIF)) // if a byte is received (SPIF=1) + first step to clear int flags

{

twobytesDR.b_form.low=SPIDR; //1st byte storage

while(ValBit(SPISR,SPIF));

twobytesDR.b_form.high=SPIDR; //2nd byte storage

}

else // then MODF flag caused the interrupt -> add your own code here

{

SPICR=0xC4; // second step to clear MODF flag: write access to SPICR (init value)

}

}

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