ATMEGA8535L-8AC Atmel, ATMEGA8535L-8AC Datasheet - Page 185

• Manufacturer Part Number: ATMEGA8535L-8AC
• Description: IC AVR MCU 8K LV 8MHZ COM 44TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA8535L-8AC

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (4K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 512 x 8
• Ram Size: 512 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Using the TWI
Figure 85. Interfacing the Application to the TWI in a Typical Transmission
2502K–AVR–10/06
TWI bus
1. Application writes
to TWCR to initiate
transmission of
START condition sent
Status code indicates
START
2. TWINT set.
START
TWINT is written to one, and TWSTA is
TWDR, and loads appropriate control
3. Check TWSR to see if START was
signals into TWCR, making sure that
sent. Application loads SLA+W into
written to zero.
The AVR TWI is byte-oriented and interrupt based. Interrupts are issued after all bus
events, like reception of a byte or transmission of a START condition. Because the TWI
is interrupt-based, the application software is free to carry on other operations during a
TWI byte transfer. Note that the TWI Interrupt Enable (TWIE) bit in TWCR together with
the Global Interrupt Enable bit in SREG allow the application to decide whether or not
assertion of the TWINT Flag should generate an interrupt request. If the TWIE bit is
cleared, the application must poll the TWINT Flag in order to detect actions on the TWI
bus.
When the TWINT Flag is asserted, the TWI has finished an operation and awaits appli-
cation response. In this case, the TWI Status Register (TWSR) contains a value
indicating the current state of the TWI bus. The application software can then decide
how the TWI should behave in the next TWI bus cycle by manipulating the TWCR and
TWDR Registers.
Figure 85 is a simple example of how the application can interface to the TWI hardware.
In this example, a Master wishes to transmit a single data byte to a Slave. This descrip-
tion is quite abstract, a more detailed explanation follows later in this section. A simple
code example implementing the desired behavior is also presented.
1. The first step in a TWI transmission is to transmit a START condition. This is
2. When the START condition has been transmitted, the TWINT Flag in TWCR is
3. The application software should now examine the value of TWSR, to make sure
SLA+W
done by 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.
set, and TWSR is updated with a status code indicating that the START condition
has successfully been sent.
that the START condition was successfully transmitted. If TWSR indicates other-
wise, the application software might take some special action, like calling an
error routine. Assuming that the status code is as expected, the application must
Status code indicates
SLA+W sent, ACK
4. TWINT set.
received
A
appropriate control signals into TWCR,
5. Check TWSR to see if SLA+W was
sent and ACK received. Application
loads data into TWDR, and loads
making sure that TWINT is
wwritten to one.
Data
data sent, ACK received
Status code indicates
6. TWINT set.
A
7. Check TWSR to see if data was sent
and ACK received. Application loads
STOP into TWCR, making sure that
appropriate control signals to send
ATmega8535(L)
TWINT is written to one.
STOP
TWINT set
Indicates
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