ATmega645P Atmel Corporation, ATmega645P Datasheet - Page 203
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ATmega645P
Manufacturer Part Number
ATmega645P
Description
Manufacturer
Atmel Corporation
Specifications of ATmega645P
Flash (kbytes)
64 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
54
Ext Interrupts
17
Usb Speed
No
Usb Interface
No
Spi
2
Twi (i2c)
1
Uart
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
No
Crypto Engine
No
Sram (kbytes)
4
Eeprom (bytes)
2048
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
3
Output Compare Channels
4
Input Capture Channels
1
Pwm Channels
4
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
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21.3.4
8285D–AVR–06/11
Two-wire Mode
ATmega165A/PA/325A/PA/3250A/PA/645A/P/6450A/P
The USI Two-wire mode is compliant to the Inter IC (TWI) bus protocol, but without slew rate lim-
iting on outputs and input noise filtering. Pin names used by this mode are SCL and SDA.
Figure 21-4. Two-wire Mode Operation, Simplified Diagram
Figure 21-4 on page 203
one as Slave. It is only the physical layer that is shown since the system operation is highly
dependent of the communication scheme used. The main differences between the Master and
Slave operation at this level, is the serial clock generation which is always done by the Master,
and only the Slave uses the clock control unit. Clock generation must be implemented in soft-
ware, but the shift operation is done automatically by both devices. Note that only clocking on
negative edge for shifting data is of practical use in this mode. The slave can insert wait states at
start or end of transfer by forcing the SCL clock low. This means that the Master must always
check if the SCL line was actually released after it has generated a positive edge.
Since the clock also increments the counter, a counter overflow can be used to indicate that the
transfer is completed. The clock is generated by the master by toggling the USCK pin via the
PORT Register.
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.
SLAVE
MASTER
Bit7
Bit7
Bit6
Bit6
Bit5
Bit5
shows two USI units operating in Two-wire mode, one as Master and
Bit4
Bit4
Bit3
Bit3
Bit2
Bit2
Bit1
Bit1
Bit0
Bit0
Two-wire Clock
Control Unit
PORTxn
HOLD
SCL
SDA
SCL
SDA
SCL
VCC
203
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