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CHAPTER 14 UART0
14.5.3
Baud rate by external clock
This section explains the setting when selecting the external clock as the transmit/
receive clock of the UART0.
I Baud rate by external clock
The following settings are required for selecting a baud rate depending on the external clock input:
• Set the clock input source select bits (SMR0: CS2 to CS0) in the serial mode register to "111
• Set the SCK0 pin as the input port in the port direction register (DDR).
• To set the SCK0 pin as an external clock input pin, set the serial clock I/O enable bit (SMR0: SCKE) to
"0".
• Set the baud rate on the basis of the external clock input from the SCK0 pin.To change the baud rate, the
external input clock cycle must be changed as the internal frequency divide ratio is fixed.
G
Calculation expression for baud rate
Asynchronous baud rate = f/16 bps
Clock synchronous baud rate = f bps
External clock frequency (2 MHz max.)
412
Figure 14.5-4 Baud Rate Selector by External Clock
SMR0: CS2 to CS0 = "111
(Clock input source select bit)
SCK0
1/1 [Clock sync]
Pin
1/16 [Asynchronous]
(Operating mode select bit)
"
B
Clock selector
SMR0: MD1, MD0
Baud rate
".
B
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