ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 223

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

9223B–AVR–09/11
Even though this example is simple, it shows the principles involved in all TWI transmissions.
These can be summarized as follows:
In the following an assembly and C implementation of the example is given. Note that the code
below assumes that several definitions have been made, for example by using include-files.
5. The application software should now examine the value of TWSR, to make sure that
6. When the data packet has been transmitted, the TWINT Flag in TWCR is set, and
7. The application software should now examine the value of TWSR, to make sure that
• When the TWI has finished an operation and expects application response, the TWINT
• When the TWINT Flag is set, the user must update all TWI Registers with the value
• After all TWI Register updates and other pending application software tasks have been
Flag is set. The SCL line is pulled low until TWINT is cleared.
relevant for the next TWI bus cycle. As an example, TWDR must be loaded with the value
to be transmitted in the next bus cycle.
completed, TWCR is written. When writing TWCR, the TWINT bit should be set. Writing a
one to TWINT clears the flag. The TWI will then commence executing whatever operation
was specified by the TWCR setting.
Atmel ATmega48PA/88PA/168PA [Preliminary]
the address packet was successfully transmitted, and that the value of the ACK bit
was as expected. If TWSR indicates otherwise, the application software might take
some special action, like calling an error routine. Assuming that the status code is as
expected, the application must load a data packet into TWDR. Subsequently, a spe-
cific value must be written to TWCR, instructing the TWI hardware to transmit the
data packet present in TWDR. Which value to write is described later on. However, it
is important that the TWINT bit is set in the value written. Writing a one to TWINT
clears the flag. The TWI will not start any operation as long as the TWINT bit in
TWCR is set. Immediately after the application has cleared TWINT, the TWI will initi-
ate transmission of the data packet.
TWSR is updated with a status code indicating that the data packet has successfully
been sent. The status code will also reflect whether a Slave acknowledged the packet
or not.
the data packet was successfully transmitted, and that the value of the ACK bit was
as expected. If TWSR indicates otherwise, the application software might take some
special action, like calling an error routine. Assuming that the status code is as
expected, the application must write a specific value to TWCR, instructing the TWI
hardware to transmit a STOP condition. Which value to write is described later on.
However, it is important that the TWINT bit is set in the value written. Writing a one to
TWINT clears the flag. The TWI will not start any operation as long as the TWINT bit
in TWCR is set. Immediately after the application has cleared TWINT, the TWI will ini-
tiate transmission of the STOP condition. Note that TWINT is NOT set after a STOP
condition has been sent.
223