ATtiny84 Atmel Corporation, ATtiny84 Datasheet - Page 122

• Manufacturer Part Number: ATtiny84
• Manufacturer: Atmel Corporation

Specifications of ATtiny84

• Flash (kbytes): 8 Kbytes
• Pin Count: 14
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 6
• Hardware Qtouch Acquisition: No
• 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): 0.5
• Eeprom (bytes): 512
• Self Program Memory: YES
• 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: 4
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

122
ATtiny24/44/84
Figure 14-4. Two-wire Mode Operation, Simplified Diagram
The data direction is not given by the physical layer. A protocol, like the one used by the TWI-
bus, must be implemented to control the data flow.
Figure 14-5. Two-wire Mode, Typical Timing Diagram
Referring to the timing diagram
SDA
SCL
1. The start condition is generated by the master by forcing the SDA low line while keep-
2. In addition, the start detector will hold the SCL line low after the master has forced a
ing the SCL line high (A). SDA can be forced low either by writing a zero to bit 7 of the
USI Data Register, or by setting the corresponding bit in the PORTA register to zero.
Note that the Data Direction Register bit must be set to one for the output to be
enabled. The start detector logic of the slave device (see
detects the start condition and sets the USISIF Flag. The flag can generate an interrupt
if necessary.
negative edge on this line (B). This allows the slave to wake up from sleep or complete
other tasks before setting up the USI Data Register to receive the address. This is done
by clearing the start condition flag and resetting the counter.
SLAVE
MASTER
S
A B
Bit7
Bit7
Bit6
Bit6
C
ADDRESS
1 - 7
Bit5
Bit5
Bit4
Bit4
Bit3
Bit3
R/W
(Figure
8
D
Bit2
Bit2
Bit1
Bit1
14-5), a bus transfer involves the following steps:
ACK
9
Bit0
Bit0
E
DATA
1 - 8
Two-wire Clock
Control Unit
ACK
9
PORTxn
Figure 14-6 on page
HOLD
SCL
DATA
1 - 8
SDA
SCL
SDA
SCL
ACK
9
VCC
8006K–AVR–10/10
123)
F
P