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Chapter 32 USART (LIN / FIFO)
6.USART Baud Rates
■ Transmission Interrupt Request Generation Timing
If the TDRE flag is set to 1 when a transmission interrupt is enabled (SSR04: TIE=1) a transmission interrupt
request is generated.
A transmission completion interrupt is generated immediately after the transmission interrupt is enabled
(TIE=1) because the TDRE bit is set to 1 as its initial value. TDRE is a read-only bit that can be cleared only
by writing new data to the output data register (TDR04). Carefully specify the transmission interrupt enable
timing.
6. USART Baud Rates
One of the following can be selected for the USART serial clock source:
• Dedicated baud rate generator (Reload Counter)
• External clock as it is (clock input to the SCK04 pin)
• External clock connected to the baud rate generator (Reload Counter)
■ USART Baud Rate Selection
The baud rate selection circuit is designed as shown below. One of the following three types of baud rates can
be selected:
• Baud Rates Determined Using the Dedicated Baud Rate Generator (Reload Counter)
USART has two independent internal reload counters for transmission and reception serial clock. The baud rate can be
selected via the 15-bit reload value determined by the Baud Rate Generator Register 0 and 1 (BGR0/1).
The reload counter divides the peripheral clock by the value set in the Baud Rate Generator Register 0 and 1.
• Baud Rates determined using external clock (one-to-one mode)
The clock input from USART clock pulse input pins (SCK04) is used as it is (synchronous). Any baud rate less than the
peripheral clock divided by 4 and is divisible can be set externally
• Baud Rates determined using the dedicated baud rate generator with external clock
An external clock source can also be connected internally to the reload counter. In this mode it is used instead of the
internal peripheral clock. This was designed to use quartz oscillators with special frequencies and having the possibility
to divide them.