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Details of Pins in Block Diagram
The actual pin names and interrupt request numbers used in the UART0 are as follows:
SCK pin: P31/SCK0/RD
TX pin: P43/TX: P30/SOT0/ALE
SIN pin: P32/SIN0/WRL
Transmit interrupt number: #39 (27
Receive interrupt number: #40 (28
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Clock selector
The clock selector selects the transmission/reception clock from among the dedicated baud rate generator,
external input clock, and internal clock (clock supplied from 16-bit reload timer 0).
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Reception control circuit
The receive controller is composed of receive bit counter, start bit detector and receive parity counter.The
receive bit counter counts received data and outputs a receive interrupt request when the reception of one
frame of data is completed.
The start bit detection circuit detects a start bit in a serial input signal and writes the received data to the
serial input data register while shifting bit by bit according to the transfer rate.The receive parity counter
calculates parity in received data.
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Transmission control circuit
The transmit controller is composed of the transmit bit counter, transmit start circuit, and transmit parity
counter.The transmit bit counter counts the data to transmit and outputs a transmission interrupt request
when the transmission of one frame of data is completed.The transmit start circuit starts transmission when
serial output data register (SODR) is written to.The transmit parity counter generates the parity bit of the
data transferred when parity is provided.
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Receive shift register
The receive shift register captures the receive data input from the SIN pin while shifting bit by bit and,
upon completion of reception, transfers the received data to the serial input data register.
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Transmit shift register
Data written to the serial output data register is transferred to the transmit shift register to output the data to
the SOT pin while shifting bit by bit.
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Serial mode register 0 (SMR0)
The serial mode register (SMR0) is used to select the operation mode, select the clock input source (baud
rate), and to enable or disable serial data and clock pin outputs.
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Serial control register (SCR)
The register is used to select whether to use parity, select the type of parity, set the stop bit length and data
length, select the frame data format in operation mode 1, clear the error flag, and to enable/disable
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CHAPTER 14 UART0
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