Rainbow-electronics ATmega3290P_V Manual do Utilizador descarregar pdf (Página 191)

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ATmega329/3290/649/6490

2552H–AVR–11/06

The following code demonstrates how to use the USI module as a SPI Master with max-

imum speed (fsck = fck/4):

SPITransfer_Fast:

sts USIDR,r16

ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)

ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)

sts USICR,r16 ; MSB

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16

sts USICR,r17

sts USICR,r16 ; LSB

sts USICR,r17

lds r16,USIDR

ret

SPI Slave Operation Example The following code demonstrates how to use the USI module as a SPI Slave:

init:

ldi r16,(1<<USIWM0)|(1<<USICS1)

sts USICR,r16

...

SlaveSPITransfer:

sts USIDR,r16

ldi r16,(1<<USIOIF)

sts USISR,r16

SlaveSPITransfer_loop:

lds r16, USISR

sbrs r16, USIOIF

rjmp SlaveSPITransfer_loop

lds r16,USIDR

ret

The code is size optimized using only eight instructions (+ ret). The code example

assumes that the DO is configured as output and USCK pin is configured as input in the

DDR Register. The value stored in register r16 prior to the function is called is trans-

1 2 ... 186 187 188 189 190 191 192 193 194 195 196 ... 374 375

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