ATMEGA8L-8PJ Atmel, ATMEGA8L-8PJ Datasheet - Page 132
ATMEGA8L-8PJ
Manufacturer Part Number
ATMEGA8L-8PJ
Description
IC MCU AVR 8K 5V 8MHZ 28-DIP
Manufacturer
Atmel
Series
AVR® ATmegar
Specifications of ATMEGA8L-8PJ
Core Processor
AVR
Core Size
8-Bit
Speed
8MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
8KB (4K x 16)
Program Memory Type
FLASH
Eeprom Size
512 x 8
Ram Size
1K x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 6x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
28-DIP (0.300", 7.62mm)
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
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Double Speed
Operation (U2X)
External Clock
Synchronous Clock
Operation
132
ATmega8(L)
Table 52. Equations for Calculating Baud Rate Register Setting
Note:
Some examples of UBRR values for some system clock frequencies are found in
page
The transfer rate can be doubled by setting the U2X bit in UCSRA. 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 (UMSEL = 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
(U2X = 0)
Asynchronous Double Speed
Mode (U2X = 1)
Synchronous Master Mode
BAUD Baud rate (in bits per second, bps)
fOSC
UBRR Contents of the UBRRH and UBRRL Registers (0 - 4095)
153.
1. The baud rate is defined to be the transfer rate in bit per second (bps)
System Oscillator clock frequency
osc
depends on the stability of the system clock source. It is therefore recommended to
Figure 62 on page 131
BAUD
BAUD
BAUD
Equation for Calculating
Baud Rate
=
for details.
=
=
f
-------------------------------------- -
16 UBRR
XCK
---------------------------------- -
8 UBRR
---------------------------------- -
2 UBRR
(
(
(
<
f
f
f
OSC
OSC
OSC
f
---------- -
(1)
OSC
4
+
+
+
1
1
1
)
)
)
Equation for Calculating
UBRR
UBRR
UBRR
UBRR Value
=
=
=
----------------------- - 1
16BAUD
------------------- - 1
8BAUD
------------------- - 1
2BAUD
f
f
f
OSC
OSC
OSC
–
–
–
2486Z–AVR–02/11
Table 60 on
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