ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 212

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Transmission Modes
212
ATmega64(L)
The TWI can operate in one of four major modes. These are named Master Transmitter
(MT), Master Receiver (MR), Slave Transmitter (ST) and Slave Receiver (SR). Several
of these modes can be used in the same application. As an example, the TWI can use
MT mode to write data into a TWI EEPROM, MR mode to read the data back from the
EEPROM. If other masters are present in the system, some of these might transmit data
to the TWI, and then SR mode would be used. It is the application software that decides
which modes are legal.
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 fig-
ures contain the following abbreviations:
In Figure 97 to Figure 103, 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 appropri-
ate software action. For each status code, the required software action and details of the
following serial transfer are given in Table 88 to Table 91. Note that the prescaler bits
are masked to zero in these tables.
S:
Rs:
R:
W:
A:
A:
Data:
P:
SLA:
START condition
REPEATED START condition
Read bit (high level at SDA)
Write bit (low level at SDA)
Acknowledge bit (low level at SDA)
Not acknowledge bit (high level at SDA)
8-bit data byte
STOP condition
Slave Address
2490G–AVR–03/04