ATtiny20 Atmel Corporation, ATtiny20 Datasheet - Page 146

• Manufacturer Part Number: ATtiny20
• Manufacturer: Atmel Corporation

Specifications of ATtiny20

• Flash (kbytes): 2 Kbytes
• Pin Count: 14
• Max. Operating Frequency: 12 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 5
• Hardware Qtouch Acquisition: Yes
• Max I/o Pins: 12
• Ext Interrupts: 12
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• 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: Yes
• Crypto Engine: No
• Sram (kbytes): 0.12
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.8 to 5.5
• Operating Voltage (vcc): 1.8 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 2
• Output Compare Channels: 4
• Input Capture Channels: 1
• Pwm Channels: 3
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

17.4.1.2
17.4.1.3
17.4.1.4
17.4.2
17.4.3
17.5
17.5.1
146
Register Description
ATtiny20
Receiving Data Packets
Transmitting Data Packets
TWSCRA – TWI Slave Control Register A
Case 2: Address packet accepted - Direction bit cleared
Case 3: Collision
Case 4: STOP condition received.
If the R/W Direction flag is cleared this indicates a master write operation. The SCL line is forced
low, stretching the bus clock. If ACK is sent by the slave, the slave will wait for data to be
received. Data, Repeated START or STOP can be received after this. If NACK is indicated the
slave will wait for a new START condition and address match.
If the slave is not able to send a high level or NACK, the Collision flag is set and it will disable the
data and acknowledge output from the slave logic. The clock hold is released. A START or
repeated START condition will be accepted.
Operation is the same as case 1 or 2 above with one exception. When the STOP condition is
received, the Slave Address/Stop flag will be set indicating that a STOP condition and not an
address match occurred.
The slave will know when an address packet with R/W direction bit cleared has been success-
fully received. After acknowledging this, the slave must be ready to receive data. When a data
packet is received the Data Interrupt Flag is set, and the slave must indicate ACK or NACK.
After indicating a NACK, the slave must expect a STOP or Repeated START condition.
The slave will know when an address packet, with R/W direction bit set, has been successfully
received. It can then start sending data by writing to the Slave Data register. When a data packet
transmission is completed, the Data Interrupt Flag is set. If the master indicates NACK, the slave
must stop transmitting data, and expect a STOP or Repeated START condition.
• Bit 7 – TWSHE: TWI SDA Hold Time Enable
When this bit is set each negative transition of SCL triggers an additional internal delay, before
the device is allowed to change the SDA line. The added delay is approximately 50ns in length.
This may be useful in SMBus systems.
• Bit 6 – Res: Reserved Bit
This bit is reserved and will always read as zero.
• Bit 5 – TWDIE: TWI Data Interrupt Enable
When this bit is set and interrupts are enabled, a TWI interrupt will be generated when the data
interrupt flag (TWDIF) in TWSSRA is set.
Bit
0x2D
Read/Write
Initial Value
TWSHE
R/W
7
0
R
6
–
0
TWDIE
R/W
5
0
TWASIE
R/W
4
0
TWEN
R/W
3
0
TWSIE
R/W
2
0
TWPME
R/W
1
0
TWSME
R/W
0
0
8235B–AVR–04/11
TWSCRA