ATMEGA168PA-PU Atmel, ATMEGA168PA-PU Datasheet - Page 179

• Manufacturer Part Number: ATMEGA168PA-PU
• Description: MCU, 8BIT, AVR, 16K FLASH, 28PDIP
• Manufacturer: Atmel

Specifications of ATMEGA168PA-PU

• Controller Family/series: Atmega
• No. Of I/o's: 23
• Eeprom Memory Size: 512Byte
• Ram Memory Size: 1KB
• Cpu Speed: 20MHz
• No.: RoHS Compliant
• Core Size: 8bit
• Program Memory Size: 16KB
• Oscillator Type: External, Internal
• Rohs Compliant: Yes

19.3.1
8271C–AVR–08/10
Internal Clock Generation – The Baud Rate Generator
Figure 19-2
Figure 19-2. Clock Generation Logic, Block Diagram
Signal description:
Internal clock generation is used for the asynchronous and the synchronous master modes of
operation. The description in this section refers to
The USART Baud Rate Register (UBRRn) and the down-counter connected to it function as a
programmable prescaler or baud rate generator. The down-counter, running at system clock
(f
the UBRRnL Register is written. A clock is generated each time the counter reaches zero. This
clock is the baud rate generator clock output (= f
baud rate generator clock output by 2, 8 or 16 depending on mode. The baud rate generator out-
put is used directly by the Receiver’s clock and data recovery units. However, the recovery units
use a state machine that uses 2, 8 or 16 states depending on mode set by the state of the
UMSELn, U2Xn and DDR_XCKn bits.
ATmega48A/48PA/88A/88PA/168A/168PA/328/328
osc
), is loaded with the UBRRn value each time the counter has counted down to zero or when
txclk
rxclk
xcki
xcko
fosc
DDR_XCKn
XCKn
Pin
shows a block diagram of the clock generation logic.
Transmitter clock (Internal Signal).
Receiver base clock (Internal Signal).
Input from XCK pin (internal Signal). Used for synchronous slave operation.
Clock output to XCK pin (Internal Signal). Used for synchronous master
operation.
XTAL pin frequency (System Clock).
xcko
xcki
OSC
Down-Counter
Prescaling
Register
UBRRn
Sync
UBRRn+1
foscn
Detector
UCPOLn
Edge
/2
Figure
osc
/(UBRRn+1)). The Transmitter divides the
/4
19-2.
/2
DDR_XCKn
U2Xn
0
1
0
1
0
1
1
0
UMSELn
txclk
rxclk
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