ATMEGA48V_06 ATMEL [ATMEL Corporation], ATMEGA48V_06 Datasheet - Page 172

• Manufacturer Part Number: ATMEGA48V_06
• Description: 8-bit Microcontroller with 8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

18.3
172
Clock Generation
ATmega48/88/168
Figure 18-1. USART Block Diagram
Note:
The Clock Generation logic generates the base clock for the Transmitter and Receiver. The
USART supports four modes of clock operation: Normal asynchronous, Double Speed asyn-
chronous, Master synchronous and Slave synchronous mode. The UMSELn bit in USART
Control and Status Register C (UCSRnC) selects between asynchronous and synchronous
operation. Double Speed (asynchronous mode only) is controlled by the U2Xn found in the
UCSRnA Register. When using synchronous mode (UMSELn = 1), the Data Direction Register
for the XCKn pin (DDR_XCKn) controls whether the clock source is internal (Master mode) or
external (Slave mode). The XCKn pin is only active when using synchronous mode.
Figure 18-2
1. Refer to
shows a block diagram of the clock generation logic.
Figure 1-1 on page 2
UCSRnA
TRANSMIT SHIFT REGISTER
RECEIVE SHIFT REGISTER
BAUD RATE GENERATOR
UDRn(Transmit)
UDRn (Receive)
UBRRn [H:L]
(1)
and
Table 12-9 on page 84
UCSRnB
GENERATOR
SYNC LOGIC
RECOVERY
RECOVERY
CHECKER
PARITY
PARITY
CLOCK
DATA
OSC
for USART0 pin placement.
Clock Generator
CONTROL
CONTROL
CONTROL
CONTROL
CONTROL
Transmitter
PIN
PIN
PIN
RX
TX
Receiver
UCSRnC
XCKn
TxDn
RxDn
2545J–AVR–12/06