Rainbow Electronics ATmega163L - Manual (Page 83)

ATmega163(L)
83
Assembly Code Example - Slave Receiver Mode
;Part specific include file and TWI include file must be included.
; <Initialize registers TWAR and TWBR>
ldi r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out TWCR, r16 ; Enable TWI in Slave Receiver Mode
; <Receive START condition and SLA+W>
wait10:in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; START followed by SLA+W has been received
rjmp wait10
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, SR_SLA_ACK ; different from SR_SLA_ACK, go to ERROR
brne ERROR
ldi r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out TWCR, r16 ; Clear TWINT bit in TWCR to start reception of first
; data byte. Setting TWEA indicates that
; ACK should be returned after receiving first data byte
wait11: in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; data has been received and ACK returned
rjmp wait11
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, SR_SLA_ACK ; different from SR_SLA_ACK, go to ERROR
brne ERROR
ldi r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out TWCR, r16 ; Clear TWINT bit in TWCR to start reception
; of data. Setting TWEA causes ACK to be
; returned after reception of next data byte
wait12:in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; data has been received and ACK returned
rjmp wait12
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, SR_DATA_ACK ; different from SR_DATA_ACK, go to ERROR
brne ERROR
in r16, TWDR ; Input received data from TWDR.
nop ;<do something with received data>
ldi r16, (1<<TWINT) | (1<<TWEN)
out TWCR, r16 ; Clear TWINT bit in TWCR to start reception of data.
; Not setting TWEA causes NACK to be
; returned after reception of next data byte
wait13:in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; data has been received and NACK returned
rjmp wait13