M38C89MB datasheet(25/55 Pages) RENESAS

25 / 55 page

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

38C8 Group

SERIAL I/O

Serial I/O can be used as either clock synchronous or asynchronous

(UART) serial I/O. A dedicated timer (baud rate generator) is also

provided for baud rate generation.

(1) Clock Synchronous Serial I/O Mode

Clock synchronous serial I/O can be selected by setting the mode

selection bit of the serial I/O control register to “1”.

For clock synchronous serial I/O, the transmitter and the receiver

must use the same clock. If an internal clock is used, transfer is started

by a write signal to the transmit/receive buffer registers.

Fig. 20 Block diagram of clock synchronous serial I/O

Fig. 21 Operation of clock synchronous serial I/O function

P46/SCLK

P47/SRDY

P44/RXD

P45/TXD

f(XIN)

1/4

F/F

Serial I/O status register

Serial I/O control register

Receive buffer register

Address 001816

Receive shift register

Receive buffer full flag (RBF)

Receive interrupt request (RI)

Clock control circuit

Shift clock

Serial I/O

clock selection bit

Frequency division ratio 1/(n+1)

Baud rate generator

Address 001C16

BRG count source selection bit

Clock control circuit

Falling-edge detector

Data bus

Address 001816

Shift clock

Transmit shift register shift completion flag (TSC)

Transmit buffer empty flag (TBE)

Transmit interrupt request (TI)

Transmit interrupt source selection bit

Address 001916

Data bus

Address 001A16

Transmit buffer register

Transmit shift register

(f(XCIN) in low-speed mode)

Receive enable signal SRDY

RBF = 1

TSC = 1

TBE = 0

TBE = 1

TSC = 0

Transmit/receive shift clock

(1/2 to 1/2048 of internal clock,

or an external clock)

Serial output TXD

Serial input RXD

Write signal to receive/transmit

buffer register (address 001816)

Overrun error (OE)

detection

Notes 1: The transmit interrupt (TI) can be selected to occur either when the transmit buffer register has emptied (TBE=1) or after

the transmit shift operation has ended (TSC=1), by setting the transmit interrupt source selection bit (TIC) of the serial

I/O control register.

2: If data is written to the transmit buffer register when TSC=0, the transmit clock is generated continuously and serial data

is output continuously from the TXD pin.

3: The receive interrupt (RI) is set when the receive buffer full flag (RBF) becomes “1” .

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