Datasheet

The following sections describe each of these modes. Possible status codes are described along with
figures detailing data transmission in each of the modes. These figures use the following abbreviations:
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
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 continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT Flag
is cleared by software.
When the TWINT Flag is set, the status code in TWSR is used to determine the appropriate software
action. For each status code, the required software action and details of the following serial transfer are
given below in the Status Code table for each mode. Note that the prescaler bits are masked to zero in
these tables.
25.6.2 Master Transmitter Mode
In the Master Transmitter (MT) mode, a number of data bytes are transmitted to a Slave Receiver, see
figure below. In order to enter a Master mode, a START condition must be transmitted. The format of the
following address packet determines whether MT or Master Receiver (MR) 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 25-11. Data Transfer in Master Transmitter Mode
Device 1
MASTER
TRANSMITTER
Device 2
SLA VE
RECEIVER
Device 3
Device n
SD A
SCL
........
R1 R2
V
CC
A START condition is sent by writing a value to the TWI Control Register (TWCR) of the type
TWCR=1x10x10x:
AVR 8-Bit Microcontroller
TWI - Two-wire Serial Interface
© 2017 Microchip Technology Inc.
Datasheet Complete
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