ATmega169P datasheet(203/393 Pages) ATMEL

Part #	ATmega169P

Description	8-bit Microcontroller with 16K Bytes In-System Programmable Flash

PDF	393 Pages

Scroll/Zoom	100%

Manufacturer	ATMEL [ATMEL Corporation]

Direct Link	http://www.atmel.com

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203 / 393 page

203

8018N–AVR–08/09

ATmega169P

20.2.3

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 transferred to the master device, and

when the transfer is completed the data received from the Master is stored back into the r16

Note that the first two instructions is for initialization only and needs only to be executed

once.These instructions sets Three-wire mode and positive edge Shift Register clock. The loop

is repeated until the USI Counter Overflow Flag is set.

ATmega169P Datasheet(PDF) 203 Page - ATMEL Corporation