Datasheet

226
7593L–AVR–09/12
AT90USB64/128
S: START condition
Rs: REPEATED START condition
R: Read bit (high level at SDA)
W: Write bit (low level at SDA)
A: Acknowledge bit (low level at SDA)
A
: Not acknowledge bit (high level at SDA)
Data: 8-bit data byte
P: STOP condition
SLA: Slave Address
In Figure 21-13 on page 229 to Figure 21-19 on page 238, circles are used to indicate that the
TWINT Flag is set. The numbers in the circles show the status code held in TWSR, with the
prescaler bits masked to zero. At these points, actions must be taken by the application to con-
tinue or complete the TWI transfer. The TWI transfer is suspended until the TWINT Flag is
cleared by softw are.
When the TWINT Flag is set, the status code in TWSR is used to determine the appropriate soft-
ware action. For each status code, the required software action and details of the following serial
transfer are given in Table 21-3 on page 227 to Table 21-6 on page 237. Note that the prescaler
bits are masked to zero in these tables.
21.8.1 Master Transmitter Mode
In the Master Transmitter mode, a number of data bytes are transmitted to a Slave Receiver
(see Figure 21-12). In order to enter a Master mode, a START condition must be transmitted.
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 trans-
mitted, 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 21-12. Data transfer in master transmitter mode.
A START condition is sent by writing the following value to TWCR:
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE
Value 1
X10X10 X
Device 1
MASTER
TRANSMITTER
Device 2
SLAVE
RECEIVER
Device 3
Device n
SDA
SCL
........
R1 R2
V
CC