ATMEGA168PA-PU Atmel, ATMEGA168PA-PU Datasheet - Page 181
![MCU, 8BIT, AVR, 16K FLASH, 28PDIP](/photos/19/6/190669/ge28pdip05-40_sml.jpg)
ATMEGA168PA-PU
Manufacturer Part Number
ATMEGA168PA-PU
Description
MCU, 8BIT, AVR, 16K FLASH, 28PDIP
Manufacturer
Atmel
Datasheet
1.ATMEGA48A-PU.pdf
(566 pages)
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
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19.3.3
19.3.4
19.4
8271C–AVR–08/10
Frame Formats
External Clock
Synchronous Clock Operation
External clocking is used by the synchronous slave modes of operation. The description in this
section refers to
External clock input from the XCKn 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 XCKn 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 (UMSELn = 1), the XCKn 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 RxDn) is sampled at the
opposite XCKn clock edge of the edge the data output (TxDn) is changed.
Figure 19-3. Synchronous Mode XCKn Timing.
The UCPOLn bit UCRSC selects which XCKn clock edge is used for data sampling and which is
used for data change. As
rising XCKn edge and sampled at falling XCKn edge. If UCPOLn is set, the data will be changed
at falling XCKn edge and sampled at rising XCKn 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:
• 1 start bit
• 5, 6, 7, 8, or 9 data bits
• no, even or odd parity bit
• 1 or 2 stop bits
ATmega48A/48PA/88A/88PA/168A/168PA/328/328
UCPOL = 1
UCPOL = 0
osc
depends on the stability of the system clock source. It is therefore recommended to
Figure 19-2
RxD / TxD
RxD / TxD
XCK
XCK
Figure 19-3
for details.
shows, when UCPOLn is zero the data will be changed at
f
XCK
<
f
---------- -
OSC
4
Sample
Sample
181
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