M38C89MB datasheet(27/55 Pages) RENESAS

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SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

38C8 Group

[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 character bit length is

7 bits, the MSB of data stored in the receive buffer register is “0”.

[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 trans-

ferred from the receive shift register to the receive buffer register,

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

the serial I/O enable bit (SIOE) also clears all the status flags, includ-

ing 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 serial

I/O function.

[UART Control Register (UARTCON)] 001B16

This is a 5 bit register containing four control bits, which are valid

when UART is selected and set the data format of an data receiver/

transfer, and one control bit, which is always valid and sets the out-

put structure of the P45/TXD pin.

[Baud Rate Generator (BRG)] 001C16

The baud rate generator determines the baud rate for serial transfer.

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 generator.

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 enabled,

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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