Spi slave operation example, Attiny2313 – Rainbow Electronics ATtiny2313 User Manual
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ATtiny2313
2543A–AVR–08/03
The following code demonstrates how to use the USI module as a SPI Master with max-
imum speed (fsck = fck/2):
SPITransfer_Fast:
out USIDR,r16
ldi r16,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)
ldi r17,(1<<USIWM0)|(0<<USICS0)|(1<<USITC)|(1<<USICLK)
out
USICR,r16 ; MSB
out USICR,r17
out
USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out USICR,r16
out USICR,r17
out
USICR,r16 ; LSB
out USICR,r17
in 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)
out
USICR,r16
...
SlaveSPITransfer:
out
USIDR,r16
ldi
r16,(1<<USIOIF)
out
USISR,r16
SlaveSPITransfer_loop:
sbis
USISR,USIOIF
rjmp
SlaveSPITransfer_loop
in
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.