ATmega165 datasheet(178/336 Pages) ATMEL

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178

ATmega165/V

2573G–AVR–07/09

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-

ferred to the master device, and when the transfer is completed the data received from

the Master is stored back into the r16 Register.

ATmega165 Datasheet(PDF) 178 Page - ATMEL Corporation

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