ATmega64 Atmel Corporation, ATmega64 Datasheet - Page 174

• Manufacturer Part Number: ATmega64
• Manufacturer: Atmel Corporation

Specifications of ATmega64

• 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: 53
• Ext Interrupts: 8
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Uart: 2
• 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: No
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 4
• Output Compare Channels: 8
• Input Capture Channels: 2
• Pwm Channels: 7
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

Double Speed
Operation (U2Xn)
External Clock
Synchronous Clock
Operation
2490Q–AVR–06/10
Table 74. Equations for Calculating Baud Rate Register Setting
Note:
Some examples of UBRRn values for some system clock frequencies are found in
page 194
The transfer rate can be doubled by setting the U2Xn bit in UCSRnB. Setting this bit only has
effect for the asynchronous operation. Set this bit to zero when using synchronous operation.
Setting this bit will reduce the divisor of the baud rate divider from 16 to 8, effectively doubling
the transfer rate for asynchronous communication. Note however that the Receiver will in this
case only use half the number of samples (reduced from 16 to 8) for data sampling and clock
recovery, and therefore a more accurate baud rate setting and system clock are required when
this mode is used. For the Transmitter, there are no downsides.
External clocking is used by the synchronous slave modes of operation. The description in this
section refers to
External clock input from the XCK pin is sampled by a synchronization register to minimize the
chance of meta-stability. The output from the synchronization register must then pass through
an edge detector before it can be used by the Transmitter and Receiver. This process intro-
duces a two CPU clock period delay and therefore the maximum external XCK clock frequency
is limited by the following equation:
Note that f
add some margin to avoid possible loss of data due to frequency variations.
When synchronous mode is used (UMSELn = 1), the XCK pin will be used as either clock input
(Slave) or clock output (Master). The dependency between the clock edges and data sampling
or data change is the same. The basic principle is that data input (on RxD) is sampled at the
opposite XCK clock edge of the edge the data output (TxD) is changed.
Operating Mode
Asynchronous Normal
mode (U2Xn = 0)
Asynchronous Double
Speed mode (U2Xn = 1)
Synchronous Master
mode
BAUD Baud rate (in bits per second, bps)
f
UBRR Contents of the UBRRnH and UBRRnL Registers, (0 - 4095)
OSC
1. The baud rate is defined to be the transfer rate in bit per second (bps).
to
System Oscillator clock frequency
osc
Table 85 on page
depends on the stability of the system clock source. It is therefore recommended to
Figure 80
for details.
BAUD
BAUD
BAUD
Equation for Calculating
197.
=
=
=
Baud Rate
----------------------------------------- -
16 UBRR
-------------------------------------- -
2 UBRR
-------------------------------------- -
8 UBRRn
(
(
(
f
XCK
f
f
f
OSC
OSC
OSC
(1)
+
<
+
+
1n
f
---------- -
OSC
1n
1
4
)
)
)
UBRRn
UBRRn
UBRRn
Equation for Calculating
UBRR Value
=
=
=
----------------------- - 1
16BAUD
ATmega64(L)
------------------- - 1
8BAUD
------------------- - 1
2BAUD
f
f
f
OSC
OSC
OSC
–
–
–
Table 82 on
174