3 spi slave operation example, 4 two-wire mode – Rainbow Electronics ATtiny861_V User Manual
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17.3.3
SPI Slave Operation Example
The following code demonstrates how to use the USI module as a SPI Slave:
init:
ldi
r16,(1< sts USICR,r16 ... SlaveSPITransfer: sts USIDR,r16 ldi r16,(1< 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 Note that the first two instructions is for initialization only and needs only to be executed 17.3.4 Two-wire Mode The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate lim-
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 transferred to the master device, and
when the transfer is completed the data received from the Master is stored back into the r16
Register.
once.These instructions sets Three-wire mode and positive edge USI Data Register clock. The
loop is repeated until the USI Counter Overflow Flag is set.
iting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.