ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 226

• Manufacturer Part Number: ATmega88PA Automotive
• Manufacturer: Atmel Corporation

226
Atmel ATmega48PA/88PA/168PA [Preliminary]
Figure 22-11. Data Transfer in Master Transmitter Mode
A START condition is sent by writing the following value to TWCR:
TWEN must be set to enable the 2-wire Serial Interface, TWSTA must be written to one to
transmit a START condition and TWINT must be written to one to clear the TWINT Flag. The
TWI will then test the 2-wire Serial Bus and generate a START condition as soon as the bus
becomes free. After a START condition has been transmitted, the TWINT Flag is set by hard-
ware, and the status code in TWSR will be 0x08 (see
SLA+W must be transmitted. This is done by writing SLA+W to TWDR. Thereafter the TWINT
bit should be cleared (by writing it to one) to continue the transfer. This is accomplished by
writing the following value to TWCR:
When SLA+W have been transmitted and an acknowledgement bit has been received, TWINT
is set again and a number of status codes in TWSR are possible. Possible status codes in
Master mode are 0x18, 0x20, or 0x38. The appropriate action to be taken for each of these
status codes is detailed in
When SLA+W has been successfully transmitted, a data packet should be transmitted. This is
done by writing the data byte to TWDR. TWDR must only be written when TWINT is high. If
not, the access will be discarded, and the Write Collision bit (TWWC) will be set in the TWCR
Register. After updating TWDR, the TWINT bit should be cleared (by writing it to one) to con-
tinue the transfer. This is accomplished by writing the following value to TWCR:
This scheme is repeated until the last byte has been sent and the transfer is ended by gener-
ating a STOP condition or a repeated START condition. A STOP condition is generated by
writing the following value to TWCR:
A REPEATED START condition is generated by writing the following value to TWCR:
TWCR
value
TWCR
value
TWCR
value
TWCR
value
TWCR
value
SDA
SCL
TWINT
TWINT
TWINT
TWINT
TWINT
1
1
1
1
1
TRANSMITTER
Device 1
MASTER
TWEA
TWEA
TWEA
TWEA
TWEA
X
X
X
X
X
Table
Device 2
RECEIVER
SLAVE
22-3.
TWSTA
TWSTA
TWSTA
TWSTA
TWSTA
1
0
0
0
1
Device 3
TWSTO
TWSTO
TWSTO
TWSTO
TWSTO
0
0
0
1
0
........
Table
TWWC
TWWC
TWWC
TWWC
TWWC
X
X
X
X
X
Device n
22-3). In order to enter MT mode,
V
CC
TWEN
TWEN
TWEN
TWEN
TWEN
1
1
1
1
1
R1
–
0
–
0
–
0
–
0
–
0
R2
9223B–AVR–09/11
TWIE
TWIE
TWIE
TWIE
TWIE
X
X
X
X
X