ATMEGA8L-8AUR Atmel, ATMEGA8L-8AUR Datasheet - Page 164
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ATMEGA8L-8AUR
Manufacturer Part Number
ATMEGA8L-8AUR
Description
MCU AVR 8KB FLASH 8MHZ 32TQFP
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheet
1.ATMEGA8L-8MU.pdf
(302 pages)
Specifications of ATMEGA8L-8AUR
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
23
Program Memory Size
8KB (4K x 16)
Program Memory Type
FLASH
Eeprom Size
512 x 8
Ram Size
1K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 8x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
*
Package
32TQFP
Device Core
AVR
Family Name
ATmega
Maximum Speed
8 MHz
Operating Supply Voltage
3.3|5 V
Data Bus Width
8 Bit
Number Of Programmable I/os
23
Interface Type
SPI/TWI/USART
On-chip Adc
8-chx10-bit
Number Of Timers
3
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Available stocks
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Manufacturer
Quantity
Price
Company:
Part Number:
ATMEGA8L-8AUR
Manufacturer:
Atmel
Quantity:
3 915
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Bit Rate Generator
Unit
Bus Interface Unit
Address Match Unit
Control Unit
164
ATmega8(L)
This unit controls the period of SCL when operating in a Master mode. The SCL period is con-
trolled by settings in the TWI Bit Rate Register (TWBR) and the Prescaler bits in the TWI Status
Register (TWSR). Slave operation does not depend on Bit Rate or Prescaler settings, but the
CPU clock frequency in the Slave must be at least 16 times higher than the SCL frequency. Note
that slaves may prolong the SCL low period, thereby reducing the average TWI bus clock
period. The SCL frequency is generated according to the following equation:
•
•
Note:
This unit contains the Data and Address Shift Register (TWDR), a START/STOP Controller and
Arbitration detection hardware. The TWDR contains the address or data bytes to be transmitted,
or the address or data bytes received. In addition to the 8-bit TWDR, the Bus Interface Unit also
contains a register containing the (N)ACK bit to be transmitted or received. This (N)ACK Regis-
ter is not directly accessible by the application software. However, when receiving, it can be set
or cleared by manipulating the TWI Control Register (TWCR). When in Transmitter mode, the
value of the received (N)ACK bit can be determined by the value in the TWSR.
The START/STOP Controller is responsible for generation and detection of START, REPEATED
START, and STOP conditions. The START/STOP controller is able to detect START and STOP
conditions even when the AVR MCU is in one of the sleep modes, enabling the MCU to wake up
if addressed by a Master.
If the TWI has initiated a transmission as Master, the Arbitration Detection hardware continu-
ously monitors the transmission trying to determine if arbitration is in process. If the TWI has lost
an arbitration, the Control Unit is informed. Correct action can then be taken and appropriate
status codes generated.
The Address Match unit checks if received address bytes match the seven-bit address in the
TWI Address Register (TWAR). If the TWI General Call Recognition Enable (TWGCE) bit in the
TWAR is written to one, all incoming address bits will also be compared against the General Call
address. Upon an address match, the Control Unit is informed, allowing correct action to be
taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR.
The Address Match unit is able to compare addresses even when the AVR MCU is in sleep
mode, enabling the MCU to wake up if addressed by a Master. If another interrupt (for example,
INT0) occurs during TWI Power-down address match and wakes up the CPU, the TWI aborts
operation and return to it’s idle state. If this cause any problems, ensure that TWI Address Match
is the only enabled interrupt when entering Power-down.
The Control unit monitors the TWI bus and generates responses corresponding to settings in the
TWI Control Register (TWCR). When an event requiring the attention of the application occurs
on the TWI bus, the TWI Interrupt Flag (TWINT) is asserted. In the next clock cycle, the TWI Sta-
tus Register (TWSR) is updated with a status code identifying the event. The TWSR only
contains relevant status information when the TWI Interrupt Flag is asserted. At all other times,
the TWSR contains a special status code indicating that no relevant status information is avail-
able. As long as the TWINT Flag is set, the SCL line is held low. This allows the application
software to complete its tasks before allowing the TWI transmission to continue.
TWBR = Value of the TWI Bit Rate Register
TWPS = Value of the prescaler bits in the TWI Status Register
Pull-up resistor values should be selected according to the SCL frequency and the capacitive bus
line load. See
Table 101 on page 238
SCL frequency
for value of pull-up resistor
=
---------------------------------------------------------- -
16
CPU Clock frequency
+
2(TWBR) 4
⋅
TWPS
2486Z–AVR–02/11
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