ATmega1281R231 Atmel Corporation, ATmega1281R231 Datasheet - Page 266

• Manufacturer Part Number: ATmega1281R231
• Manufacturer: Atmel Corporation

Specifications of ATmega1281R231

• Flash (kbytes): 128 Kbytes
• Max. Operating Frequency: 16 MHz
• Max I/o Pins: 54
• Spi: 3
• Twi (i2c): 1
• Uart: 2
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Crypto Engine: AES
• Sram (kbytes): 8
• Eeprom (bytes): 4096
• Operating Voltage (vcc): 1.8 to 3.6
• Timers: 6
• Frequency Band: 2.4 GHz
• Max Data Rate (mb/s): 2
• Antenna Diversity: Yes
• External Pa Control: Yes
• Power Output (dbm): 3
• Receiver Sensitivity (dbm): -101
• Receive Current Consumption (ma): 13.2
• Transmit Current Consumption (ma): 14.4
• Link Budget (dbm): 104

24.9
24.9.1
24.9.2
2549N–AVR–05/11
Register Description
TWBR – TWI Bit Rate Register
TWCR – TWI Control Register
•
This is summarized in
Figure 24-21. Possible Status Codes Caused by Arbitration
• Bits 7:0 – TWI Bit Rate Register
TWBR selects the division factor for the bit rate generator. The bit rate generator is a frequency
divider which generates the SCL clock frequency in the Master modes. See
Unit” on page 247
The TWCR is used to control the operation of the TWI. It is used to enable the TWI, to initiate a
Master access by applying a START condition to the bus, to generate a Receiver acknowledge,
to generate a stop condition, and to control halting of the bus while the data to be written to the
bus are written to the TWDR. It also indicates a write collision if data is attempted written to
TWDR while the register is inaccessible.
Bit
(0xB8)
Read/Write
Initial Value
Bit
(0xBC)
Read/Write
Initial Value
Two or more masters are accessing different slaves. In this case, arbitration will occur in the
SLA bits. Masters trying to output a one on SDA while another Master outputs a zero will
lose the arbitration. Masters losing arbitration in SLA will switch to Slave mode to check if
they are being addressed by the winning Master. If addressed, they will switch to SR or ST
mode, depending on the value of the READ/WRITE bit. If they are not being addressed, they
will switch to not addressed Slave mode or wait until the bus is free and transmit a new
START condition, depending on application software action.
START
TWBR7
TWINT
R/W
R/W
7
0
7
0
for calculating bit rates.
Address / General Call
Figure
Direction
received
Own
TWBR6
TWEA
Yes
R/W
R/W
Arbitration lost in SLA
6
0
6
0
SLA
24-21. Possible status values are given in circles.
Write
Read
ATmega640/1280/1281/2560/2561
TWBR5
TWSTA
No
R/W
R/W
5
0
5
0
TWBR4
TWSTO
R/W
R/W
4
0
4
0
68/78
38
B0
Arbitration lost in Data
TWBR3
TWWC
TWI bus will be released and not addressed slave mode will be entered
A START condition will be transmitted when the bus becomes free
Data byte will be received and NOT ACK will be returned
Data byte will be received and ACK will be returned
Last data byte will be transmitted and NOT ACK should be received
Data byte will be transmitted and ACK should be received
R/W
R
3
0
3
0
Data
TWBR2
TWEN
R/W
R/W
2
0
2
0
TWBR1
R/W
R
1
0
1
–
0
“Bit Rate Generator
TWBR0
TWIE
R/W
R/W
0
0
0
0
STOP
TWBR
TWCR
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