ATmega88PA Automotive Atmel Corporation, ATmega88PA Automotive Datasheet - Page 222

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

Figure 22-10. Interfacing the Application to the TWI in a Typical Transmission
222
Atmel ATmega48PA/88PA/168PA [Preliminary]
writes to TWCR to
TWI bus
transmission of
1. Application
START condition sent
Status code indicates
START
initiate
2. TWINT set.
START
TWDR, and loads appropriate control
3. Check TWSR to see if START was
signals into TWCR, makin sure that
sent. Application loads SLA+W into
1. The first step in a TWI transmission is to transmit a START condition. This is done by
2. When the START condition has been transmitted, the TWINT Flag in TWCR is set,
3. The application software should now examine the value of TWSR, to make sure that
4. When the address packet has been transmitted, the TWINT Flag in TWCR is set, and
and TWSTA is written to zero.
TWINT is written to one,
writing a specific value into TWCR, instructing the TWI hardware to transmit a START
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 initiate transmission of the
START condition.
and TWSR is updated with a status code indicating that the START condition has
successfully been sent.
the START condition was successfully transmitted. 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 SLA+W into
TWDR. Remember that TWDR is used both for address and data. After TWDR has
been loaded with the desired SLA+W, a specific value must be written to TWCR,
instructing the TWI hardware to transmit the SLA+W 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 oper-
ation as long as the TWINT bit in TWCR is set. Immediately after the application has
cleared TWINT, the TWI will initiate transmission of the address packet.
TWSR is updated with a status code indicating that the address packet has success-
fully been sent. The status code will also reflect whether a Slave acknowledged the
packet or not.
SLA+W
Status code indicates
SLA+W sent, ACK
4. TWINT set.
received
A
Application loads data into TWDR, and
5. Check TWSR to see if SLA+W was
loads appropriate control signals into
TWCR, making sure that TWINT is
sent and ACK received.
written to one
Data
data sent, ACK received
Status code indicates
6. TWINT set.
A
making sure that TWINT is written to one
7. Check TWSR to see if data was sent
Application loads appropriate control
signals to send STOP into TWCR,
STOP
and ACK received.
TWINT set
Indicates
9223B–AVR–09/11