ATMEGA48-20AJ Atmel, ATMEGA48-20AJ Datasheet - Page 173

• Manufacturer Part Number: ATMEGA48-20AJ
• Description: IC AVR MCU 4K 5V 20MHZ 32-TQFP
• Manufacturer: Atmel
• Series: AVR® ATmegar

Specifications of ATMEGA48-20AJ

• Core Processor: AVR
• Core Size: 8-Bit
• Speed: 20MHz
• Connectivity: I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, PWM, WDT
• Number Of I /o: 23
• Program Memory Size: 4KB (2K x 16)
• Program Memory Type: FLASH
• Eeprom Size: 256 x 8
• Ram Size: 512 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: 32-TQFP, 32-VQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ATMEGA48-24AJ; ATMEGA48-24AJ

19.3.2
2545S–AVR–07/10
Double Speed Operation (U2Xn)
Table 19-1
ing the UBRRn value for each mode of operation using an internally generated clock source.
Table 19-1.
Note:
Some examples of UBRRn values for some system clock frequencies are found in
(see
The transfer rate can be doubled by setting the U2Xn bit in UCSRnA. 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.
Operating Mode
Asynchronous Normal mode
(U2Xn = 0)
Asynchronous Double Speed
mode (U2Xn = 1)
Synchronous Master mode
page
BAUD
f
UBRRn
OSC
1. The baud rate is defined to be the transfer rate in bit per second (bps)
194).
contains equations for calculating the baud rate (in bits per second) and for calculat-
Equations for Calculating Baud Rate Register Setting
Baud rate (in bits per second, bps)
System Oscillator clock frequency
Contents of the UBRRnH and UBRRnL Registers, (0-4095)
Equation for Calculating Baud
BAUD
BAUD
BAUD
=
=
=
Rate
----------------------------------------- -
16 UBRRn
-------------------------------------- -
8 UBRRn
-------------------------------------- -
2 UBRRn
(
(
(
(1)
f
f
f
OSC
OSC
OSC
+
+
+
1
1
1
)
)
)
ATmega48/88/168
UBRRn
UBRRn
UBRRn
Equation for Calculating
UBRRn Value
=
=
=
----------------------- - 1
16BAUD
------------------- - 1
8BAUD
------------------- - 1
2BAUD
f
f
f
OSC
OSC
OSC
Table 19-9
–
–
–
173