38K2 Datasheet, PDF(21/151 Page) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

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38K2 Datasheet, PDF (21/151 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

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38K2 Group

SERIAL INTERFACE

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 (bit 6 of ad-

dress 0FE016) to â1â.

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 Trancemit/Receive buffer register.

P40/EXDREQ/RxD

P42/EXTC/SCLK

System clock

P43/EXA1/SRDY

P41/EXDACK/TxD

Data bus

Address 002616

Receive buffer register

Serial I/O control register

Address 0FE016

Receive buffer full flag (RBF)

Receive shift register

Shift clock

Receive interrupt request (RI)

Clock control circuit

BRG count source selection bit

1/4

Serial I/O synchronous

clock selection bit

Frequency division ratio 1/(n+1)

Baud rate generator

1/4

Address 0FE216

F/F

Falling-edge detector

Clock control circuit

Shift clock

Transmit shift register shift completion flag (TSC)

Transmit interrupt source selection bit

Transmit shift register

Transmit interrupt request (TI)

Transmit buffer register

Address 002616

Data bus

Transmit buffer empty flag (TBE)

Serial I/O status register

Address 002716

Fig. 18 Block diagram of clock synchronous serial I/O

Transfer shift clock

(1/2 to 1/2048 of the internal

clock, or an external clock)

Serial output

TXD

Serial input

RXD

Receive enable signal SRDY

Write signal to receive/transmit

buffer register (address 002616)

TBE = 0

TBE = 1

TSC = 0

RBF = 1

TSC = 1

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/O1 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 â1â .

Fig. 19 Operation of clock synchronous serial I/O function

Rev.3.00 Oct 15, 2006 page 21 of 147

REJ03B0193-0300

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