38K2 datasheet(21/151 Pages) RENESAS

21 / 151 page

38K2 Group

Rev.3.00

Oct 15, 2006

page 21 of 147

REJ03B0193-0300

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 “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 Trancemit/Receive buffer register.

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

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

P42/EXTC/SCLK

P43/EXA1/SRDY

P40/EXDREQ/RxD

System clock

1/4

F/F

Serial I/O status register

Serial I/O control register

Receive buffer register

Address 002616

Receive shift register

Receive buffer full flag (RBF)

Receive interrupt request (RI)

Clock control circuit

Shift clock

Serial I/O synchronous

clock selection bit

Frequency division ratio 1/(n+1)

Baud rate generator

Address 0FE216

BRG count source selection bit

Clock control circuit

Falling-edge detector

Data bus

Address 002616

Shift clock

Transmit shift register shift completion flag (TSC)

Transmit buffer empty flag (TBE)

Transmit interrupt request (TI)

Transmit interrupt source selection bit

Address 002716

Data bus

Address 0FE016

Transmit buffer register

Transmit shift register

P41/EXDACK/TxD

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 002616)

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 “1” .

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