3825 datasheet(29/71 Pages) RENESAS

29 / 71 page

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

3825 Group

SERIAL I/O

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

nous (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 mode 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 TB/RB (address 001816).

Fig. 23 Block diagram of clock synchronous serial I/O

Fig. 24 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 synchronization

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 (TB)

Transmit shift register

(f(XCIN) in low-speed mode)

Receive enable signal SRDY

RBF = 1

TSC = 1

TBE = 0

TBE = 1

TSC = 0

Transfer shift clock

(1/2 to 1/2048 of the 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 generated 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” .

3825 Datasheet(PDF) 29 Page - Renesas Technology Corp

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