ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 229

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

22.7.2
9223B–AVR–09/11
Master Receiver Mode
In the Master Receiver mode, a number of data bytes are received from a Slave Transmitter
(Slave see
mitted. The format of the following address packet determines whether Master Transmitter or
Master Receiver mode is to be entered. If SLA+W is transmitted, MT mode is entered, if
SLA+R is transmitted, MR mode is entered. All the status codes mentioned in this section
assume that the prescaler bits are zero or are masked to zero.
Figure 22-13. Data Transfer in Master Receiver Mode
A START condition is sent by writing the following value to TWCR:
TWEN must be written to one to enable the 2-wire Serial Interface, TWSTA must be written to
one to transmit a START condition and TWINT must be set 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+R must be transmitted. This is done by writing SLA+R 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+R 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 0x38, 0x40, or 0x48. The appropriate action to be taken for each of these
status codes is detailed in
when the TWINT Flag is set high by hardware. This scheme is repeated until the last byte has
been received. After the last byte has been received, the MR should inform the ST by sending
a NACK after the last received data byte. The transfer is ended by generating a STOP condi-
tion or a repeated START condition. A STOP condition is generated by writing the following
value to TWCR:
TWCR
value
TWCR
value
TWCR
value
Atmel ATmega48PA/88PA/168PA [Preliminary]
SDA
SCL
Figure
TWINT
TWINT
TWINT
1
1
1
Device 1
22-13). In order to enter a Master mode, a START condition must be trans-
RECEIVER
MASTER
TWEA
TWEA
TWEA
X
X
X
Table
TRANSMITTER
Device 2
SLAVE
22-4. Received data can be read from the TWDR Register
TWSTA
TWSTA
TWSTA
1
0
0
Device 3
TWSTO
TWSTO
TWSTO
0
0
1
........
Table
TWWC
TWWC
TWWC
X
X
X
Device n
22-3). In order to enter MR mode,
V
CC
TWEN
TWEN
TWEN
1
1
1
R1
–
0
–
0
–
0
R2
TWIE
TWIE
TWIE
X
X
X
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