atmega3250v-8auatmega325v-8ai ATMEL Corporation, atmega3250v-8auatmega325v-8ai Datasheet - Page 161

• Manufacturer Part Number: atmega3250v-8auatmega325v-8ai
• Description: Atmega3250 8-bit Microcontroller With In-system Programmable Flash
• Manufacturer: ATMEL Corporation

20.4
2570L–AVR–08/07
Frame Formats
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.
Figure 20-3. Synchronous Mode XCK Timing.
The UCPOLn bit in UCSRnC selects which XCK clock edge is used for data sampling and which
is used for data change. As
at rising XCK edge and sampled at falling XCK edge. If UCPOLn is set, the data will be changed
at falling XCK edge and sampled at rising XCK edge.
A serial frame is defined to be one character of data bits with synchronization bits (start and stop
bits), and optionally a parity bit for error checking. The USART accepts all 30 combinations of
the following as valid frame formats:
•
•
•
•
A frame starts with the start bit followed by the least significant data bit. Then the next data bits,
up to a total of nine, are succeeding, ending with the most significant bit. If enabled, the parity bit
is inserted after the data bits, before the stop bits. When a complete frame is transmitted, it can
be directly followed by a new frame, or the communication line can be set to an idle (high) state.
Figure 20-4
optional.
1 start bit
5, 6, 7, 8, or 9 data bits
no, even or odd parity bit
1 or 2 stop bits
UCPOL = 1
UCPOL = 0
illustrates the possible combinations of the frame formats. Bits inside brackets are
RxD / TxD
RxD / TxD
XCK
XCK
Figure 20-3
shows, when UCPOLn is zero the data will be changed
ATmega325/3250/645/6450
Sample
Sample
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