ATtiny88 Atmel Corporation, ATtiny88 Datasheet - Page 154
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ATtiny88
Manufacturer Part Number
ATtiny88
Description
Manufacturer
Atmel Corporation
Specifications of ATtiny88
Flash (kbytes)
8 Kbytes
Pin Count
32
Max. Operating Frequency
12 MHz
Cpu
8-bit AVR
# Of Touch Channels
12
Hardware Qtouch Acquisition
No
Max I/o Pins
28
Ext Interrupts
28
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)
64
Self Program Memory
YES
Dram Memory
No
Nand Interface
No
Picopower
Yes
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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15.8.6
15.9
154
Multi-master Systems and Arbitration
ATtiny48/88
Combining Several TWI Modes
In some cases, several TWI modes must be combined in order to complete the desired action.
Consider for example reading data from a serial EEPROM. Typically, such a transfer involves
the following steps:
Note that data is transmitted both from Master to Slave and vice versa. The Master must instruct
the Slave what location it wants to read, requiring the use of the MT mode. Subsequently, data
must be read from the Slave, implying the use of the MR mode. Thus, the transfer direction must
be changed. The Master must keep control of the bus during all these steps, and the steps
should be carried out as an atomical operation. If this principle is violated in a multi master sys-
tem, another Master can alter the data pointer in the EEPROM between steps 2 and 3, and the
Master will read the wrong data location. Such a change in transfer direction is accomplished by
transmitting a REPEATED START between the transmission of the address byte and reception
of the data. After a REPEATED START, the Master keeps ownership of the bus. The following
figure shows the flow in this transfer.
Figure 15-19. Combining Several TWI Modes to Access a Serial EEPROM
If multiple masters are connected to the same bus, transmissions may be initiated simultane-
ously by one or more of them. The TWI standard ensures that such situations are handled in
such a way that one of the masters will be allowed to proceed with the transfer, and that no data
will be lost in the process. An example of an arbitration situation is depicted below, where two
masters are trying to transmit data to a Slave Receiver.
1. The transfer must be initiated.
2. The EEPROM must be instructed what location should be read.
3. The reading must be performed.
4. The transfer must be finished.
S
S = START
Transmitted from master to slave
SLA+W
A
Master Transmitter
ADDRESS
A
Rs = REPEATED START
Rs
Transmitted from slave to master
SLA+R
A
Master Receiver
DATA
8008H–AVR–04/11
P = STOP
A
P