ATmega325 Atmel Corporation, ATmega325 Datasheet - Page 190

• Manufacturer Part Number: ATmega325
• Manufacturer: Atmel Corporation

Specifications of ATmega325

• Flash (kbytes): 32 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): 2
• Eeprom (bytes): 1024
• 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: 3
• Output Compare Channels: 4
• Input Capture Channels: 1
• Pwm Channels: 4
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

2570N–AVR–05/11
Figure 21-4. Two-wire Mode Operation, Simplified Diagram
Figure 21-4
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 software, 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.
Figure 21-5. Two-wire Mode, Typical Timing Diagram
Referring to the timing diagram (Figure 21-5.), a bus transfer involves the following steps:
SDA
SCL
SLAVE
MASTER
shows two USI units operating in Two-wire mode, one as Master and one as Slave.
Bit7
Bit7
A B
S
Bit6
Bit6
Bit5
Bit5
C
ADDRESS
1 - 7
Bit4
Bit4
Bit3
Bit3
R/W
8
Bit2
Bit2
D
Bit1
Bit1
ACK
9
Bit0
Bit0
E
ATmega325/3250/645/6450
DATA
1 - 8
Two-wire Clock
Control Unit
ACK
9
PORTxn
DATA
1 - 8
HOLD
SCL
SDA
SCL
SDA
SCL
ACK
9
VCC
P
F
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