Rainbow Electronics ATmega163L - Manual (Page 86)

ATmega163(L)
86
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, ST_DATA_ACK ; different from ST_DATA_ACK, go to ERROR
brne ERROR
ldi r16, 0x44 ; Load data (here, data = 0x44) into TWDR register
out TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out TWCR, r16 ; Clear TWINT bit in TWCR to start transmission of data.
; Setting TWEA indicates that ACK
; should be received when transfer finished
wait16: in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; data has been transmitted, and ACK/NACK has
rjmp wait16 ; been received
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, ST_DATA_ACK ; different from ST_DATA_ACK, go to ERROR
brne ERROR
ldi r16, 0x55 ; Load data (here, data = 0x55) into TWDR register
out TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
out TWCR, r16 ; Clear TWINT bit in TWCR to start transmission of data.
; Not setting TWEA indicates that
; NACK should be received after data byte (Master
; signalling end of transmission)
wait17: in r16,TWCR ; Wait for TWINT flag set. This indicates that
sbrs r16, TWINT ; data has been transmitted, and ACK/NACK has
rjmp wait17 ; been received
in r16, TWSR ; Check value of TWI Status Register. If status
cpi r16, ST_LAST_DATA ; different from ST_LAST_DATA, go to ERROR
brne ERROR
ldi r16, (1<<TWINT) | (1<<TWEA) | (1<<TWEN)
out TWCR, r16 ; Continue address reckognition in Slave Transmitter mode
Table 36. Status Codes for Miscellaneous States
Status code
(TWSR)
Status of the 2-wire Serial Bus
and 2-wire Serial Interface
hardware
Application software response
Next action taken by 2-wire Serial Interface hardware
To/from TWDR
To TWCR
STA STO TWINT TWEA
$F8 No relevant state information
available; TWINT = ‘0’
No TWDR action No TWCR action Wait or proceed current transfer
$00 Bus error due to an illegal
START or STOP condition
No TWDR action 0 1 1 X Only the internal hardware is affected, no STOP condi-
tion is sent on the bus. In all cases, the bus is released
and TWSTO is cleared.