ATMEGA3250P-20AU Atmel, ATMEGA3250P-20AU Datasheet - Page 196

• Manufacturer Part Number: ATMEGA3250P-20AU
• Description: IC MCU AVR 32K FLASH 100-TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA3250P-20AU

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: SPI, UART/USART, USI
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 69
• Program Memory Size: 32KB (16K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Data Converters: A/D 8x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 100-TQFP, 100-VQFP
• Processor Series: ATMEGA32x
• Core: AVR8
• Data Bus Width: 8 bit
• Data Ram Size: 2 KB
• Interface Type: SPI/UART/USI
• Maximum Clock Frequency: 20 MHz
• Number Of Programmable I/os: 69
• Number Of Timers: 3
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: EWAVR, EWAVR-BL
• Development Tools By Supplier: ATAVRDRAGON, ATSTK500, ATSTK600, ATAVRISP2, ATAVRONEKIT
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 8-ch x 10-bit
• For Use With: ATSTK600-TQFP100 - STK600 SOCKET/ADAPTER 100-TQFP770-1007 - ISP 4PORT ATMEL AVR MCU SPI/JTAG770-1005 - ISP 4PORT FOR ATMEL AVR MCU JTAG770-1004 - ISP 4PORT FOR ATMEL AVR MCU SPIATAVRISP2 - PROGRAMMER AVR IN SYSTEMATSTK504 - STARTER KIT AVR EXP MOD 100P LCD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ATMEGA3250P-16AU; ATMEGA3250P-16AU

19.3.4
196
ATmega325P/3250P
Two-wire Mode
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 19-4. Two-wire Mode Operation, Simplified Diagram
Figure 19-4
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.
SLAVE
MASTER
shows two USI units operating in Two-wire mode, one as Master and one as Slave.
Bit7
Bit7
Bit6
Bit6
Bit5
Bit5
Bit4
Bit4
Bit3
Bit3
Bit2
Bit2
Bit1
Bit1
Bit0
Bit0
Two-wire Clock
Control Unit
PORTxn
HOLD
SCL
SDA
SCL
SDA
SCL
VCC
8023F–AVR–07/09