MEGA128CAN Datasheet, PDF (213/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

AT90CAN128
set. Writing a one to TWINT clears the flag. The TWI will then commence executing
whatever operation was specified by the TWCR setting.
In the following an assembly and C implementation of the example is given. Note that
the code below assumes that several definitions have been made for example by using
include-files.
Assembly Code Example
C Example
Comments
1
ldi r16, (1<<TWINT)|(1<<TWSTA)|
TWCR = (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
(1<<TWEN)
Send START condition
sts TWCR, r16
2
wait1:
lds r16,TWCR
sbrs r16,TWINT
while (!(TWCR & (1<<TWINT)))
;
Wait for TWINT flag set. This indicates that
the START condition has been transmitted
rjmp wait1
3
lds r16,TWSR
andi r16, 0xF8
cpi r16, START
brne ERROR
if ((TWSR & 0xF8) != START)
ERROR();
Check value of TWI Status Register. Mask
prescaler bits. If status different from START
go to ERROR
ldi r16, SLA_W
sts TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
sts TWCR, r16
TWDR = SLA_W;
TWCR = (1<<TWINT) | (1<<TWEN);
Load SLA_W into TWDR Register. Clear
TWINT bit in TWCR to start transmission of
address
4
wait2:
lds r16,TWCR
sbrs r16,TWINT
rjmp wait2
while (!(TWCR & (1<<TWINT)))
;
Wait for TWINT flag set. This indicates that
the SLA+W has been transmitted, and
ACK/NACK has been received.
5
lds r16,TWSR
andi r16, 0xF8
cpi r16, MT_SLA_ACK
brne ERROR
if ((TWSR & 0xF8) != MT_SLA_ACK)
ERROR();
Check value of TWI Status Register. Mask
prescaler bits. If status different from
MT_SLA_ACK go to ERROR
ldi r16, DATA
TWDR = DATA;
sts TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
TWCR = (1<<TWINT) | (1<<TWEN);
Load DATA into TWDR Register. Clear TWINT
bit in TWCR to start transmission of data
sts TWCR, r16
6
wait3:
lds r16,TWCR
sbrs r16,TWINT
rjmp wait3
while (!(TWCR & (1<<TWINT)))
;
Wait for TWINT flag set. This indicates that
the DATA has been transmitted, and
ACK/NACK has been received.
7
lds r16,TWSR
andi r16, 0xF8
cpi r16, MT_DATA_ACK
brne ERROR
if ((TWSR & 0xF8) != MT_DATA_ACK)
ERROR();
Check value of TWI Status Register. Mask
prescaler bits. If status different from
MT_DATA_ACK go to ERROR
ldi r16, (1<<TWINT)|(1<<TWEN)|
TWCR = (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO)
(1<<TWSTO);
Transmit STOP condition
sts TWCR, r16
4250E–CAN–12/04
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