ATtiny40 Atmel Corporation, ATtiny40 Datasheet - Page 136
ATtiny40
Manufacturer Part Number
ATtiny40
Description
Manufacturer
Atmel Corporation
Specifications of ATtiny40
Flash (kbytes)
4 Kbytes
Pin Count
20
Max. Operating Frequency
12 MHz
Cpu
8-bit AVR
# Of Touch Channels
12
Hardware Qtouch Acquisition
Yes
Max I/o Pins
18
Ext Interrupts
18
Usb Speed
No
Usb Interface
No
Spi
1
Twi (i2c)
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
12
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
0.25
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
2
32khz Rtc
No
Calibrated Rc Oscillator
Yes
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17.3.8
17.3.9
136
ATtiny40
Arbitration
Synchronization
In the case where the slave is stretching the clock the master will be forced into a wait-state until
the slave is ready and vice versa.
A master can only start a bus transaction if it has detected that the bus is idle. As the TWI bus is
a multi master bus, it is possible that two devices initiate a transaction at the same time. This
results in multiple masters owning the bus simultaneously. This is solved using an arbitration
scheme where the master loses control of the bus if it is not able to transmit a high level on the
SDA line. The masters who lose arbitration must then wait until the bus becomes idle (i.e. wait
for a STOP condition) before attempting to reacquire bus ownership. Slave devices are not
involved in the arbitration procedure.
Figure 17-9. TWI Arbitration
Figure 17-9
devices are able to issue a START condition, but DEVICE1 loses arbitration when attempting to
transmit a high level (bit 5) while DEVICE2 is transmitting a low level.
Arbitration between a repeated START condition and a data bit, a STOP condition and a data
bit, or a repeated START condition and STOP condition are not allowed and will require special
handling by software.
A clock synchronization algorithm is necessary for solving situations where more than one mas-
ter is trying to control the SCL line at the same time. The algorithm is based on the same
principles used for clock stretching previously described.
two masters are competing for the control over the bus clock. The SCL line is the wired-AND
result of the two masters clock outputs.
DEVICE1_SDA
DEVICE2_SDA
SDA
(wired-AND)
SCL
shows an example where two TWI masters are contending for bus ownership. Both
S
DEVICE1 Loses arbitration
bit 7
Figure 17-10
bit 6
bit 5
shows an example where
bit 4
8263A–AVR–08/10
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