ATmega128A Atmel Corporation, ATmega128A Datasheet - Page 226

• Manufacturer Part Number: ATmega128A
• Manufacturer: Atmel Corporation

Specifications of ATmega128A

• Flash (kbytes): 128 Kbytes
• Pin Count: 64
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 53
• Ext Interrupts: 8
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 2
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 4
• Eeprom (bytes): 4096
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 8
• Input Capture Channels: 2
• Pwm Channels: 7
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

21.9
21.9.1
21.9.2
8151H–AVR–02/11
Register Description
TWBR - TWI Bit Rate Register
TWCR - TWI Control Register
This is summarized in
Figure 21-20. 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 207
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
Bit
Read/Write
Initial Value
Bit
Read/Write
Initial Value
• Two or more masters are accessing different slaves. In this case, arbitration will occur in the
Losing masters 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.
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
TWBR6
received
Direction
TWEA
R/W
R/W
Own
6
0
6
0
Yes
Arbitration lost in SLA
SLA
21-20. Possible status values are given in circles.
Write
Read
TWBR5
TWSTA
R/W
R/W
No
5
0
5
0
TWBR4
TWSTO
R/W
R/W
4
0
4
0
68/78
38
B0
Arbitration lost in Data
TWBR3
TWWC
R/W
R
3
0
3
0
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
TWBR2
TWEN
R/W
R/W
2
0
2
0
Data
TWBR1
ATmega128A
R/W
R
1
–
0
1
0
“Bit Rate Generator
TWBR0
TWIE
R/W
R/W
0
0
0
0
STOP
TWCR
TWBR
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