3822 datasheet(28/59 Pages) RENESAS

28 / 59 page

Rev.1.20

Dec 24, 2003

page 28 of 57

3822 Group (A ver.)

[Transmit Buffer/Receive Buffer Register

(TB/RB)] 001816

The transmit buffer register and the receive buffer register are lo-

cated at the same address. The transmit buffer register is

write-only and the receive buffer register is read-only. If a charac-

ter bit length is 7 bits, the MSB of data stored in the receive buffer

[Serial I/O Status Register (SIOSTS)] 001916

The read-only serial I/O status register consists of seven flags

(bits 0 to 6) which indicate the operating status of the serial I/O

function and various errors.

Three of the flags (bits 4 to 6) are valid only in UART mode.

The receive buffer full flag (bit 1) is cleared to “0” when the receive

buffer is read.

If there is an error, it is detected at the same time that data is

transferred from the receive shift register to the receive buffer reg-

ister, and the receive buffer full flag is set. A write to the serial I/O

status register clears all the error flags OE, PE, FE, and SE. Writ-

ing “0” to the serial I/O enable bit (SIOE) also clears all the status

flags, including the error flags.

All bits of the serial I/O status register are initialized to “0” at reset,

but if the transmit enable bit (bit 4) of the serial I/O control register

has been set to “1”, the transmit shift register shift completion flag

(bit 2) and the transmit buffer empty flag (bit 0) become “1”.

[Serial I/O Control Register (SIOCON)] 001A16

The serial I/O control register contains eight control bits for the se-

rial I/O function.

[UART Control Register (UARTCON) ]001B16

The UART control register consists of four control bits (bits 0 to 3)

which are valid when asynchronous serial I/O is selected and set

the data format of an data transfer. One bit in this register (bit 4) is

always valid and sets the output structure of the P45/TXD pin.

[Baud Rate Generator (BRG)] 001C16

The baud rate generator determines the baud rate for serial trans-

fer.

The baud rate generator divides the frequency of the count source

by 1/(n + 1), where n is the value written to the baud rate genera-

tor.

sNotes on serial I/O

When setting the transmit enable bit to “1”, the serial I/O transmit

interrupt request bit is automatically set to “1”. When not requiring

the interrupt occurrence synchronized with the transmission

enalbed, take the following sequence.

➀Set the serial I/O transmit interrupt enable bit to “0” (disabled).

➁Set the transmit enable bit to “1”.

➂Set the serial I/O transmit interrupt request bit to “0” after 1 or

more instructions have been executed.

➃Set the serial I/O transmit interrupt enable bit to “1” (enabled).

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