M38B74FD datasheet(39/110 Pages) RENESAS

39 / 110 page

38B7 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

(2) Asynchronous serial I/O (UART) mode

The asynchronous serial I/O (UART) mode can be selected by

clearing the serial I/O2 mode selection bit (b6) of the serial I/O2

control register (address 001D16) to “0”. Eight serial data transfer

formats can be selected and the transfer formats used by the

transmitter and receiver must be identical.

The transmit and receive shift registers each have a buffer (the

two buffers have the same address in memory). Since the shift

written to the transmit buffer, and receive data is read from the re-

ceive buffer. The transmit buffer can also hold the next data to be

transmitted, and the receive buffer can receive 2-byte data con-

tinuously.

Fig. 39 Operation of UART serial I/O2 function

Fig. 38 Block diagram of UART serial I/O2

PE FE

1/16

Transmit buffer register

Clock control circuit

P66/SCLK21

P64/RXD

P65/TXD

P67/SRDY2/SCLK22

“0”

“1”

1/4

“0”

“1”

XIN

1/2

XCIN

“1”

Data bus

Receive buffer register

Address 001F16

Receive shift register

Receive buffer full flag (RBF)

Receive interrupt request (RI)

Baud rate generator

Division ratio 1/(n+1)

Address 003716

ST/SP/PA generator

Data bus

Transmit shift register

Address 001F16

Transmit shift register shift

completion flag (TSC)

Transmit buffer empty flag (TBE)

Transmit interrupt request (TI)

Address 001E16

ST detector

UART control register

Address 003816

Character length selection bit

Address 001D16

BRG count source

selection bit

Transmit interrupt source selection bit

Serial I/O2 synchronous

clock selection bit

Character length selection bit

7 bit

8 bit

Serial I/O2 control register

Serial I/O2 status register

SP detector

Serial I/O2 clock I/O pin

selection bit

Internal system clock selection bit

BRG clock

switch bit

TSC=0

TBE=1

RBF=0

TBE=0

RBF=1

TBE=1

TSC=1*

Transmit or receive clock

* Generated at 2nd bit in 2-stop

bit mode

1 start bit

7 or 8 data bit

1 or 0 parity bit

1 or 2 stop bit

Serial I/O2 input RXD

Write-in signal to

transmit buffer register

Serial I/O2 output TXD

Read-out signal from receive

buffer register

M38B74FD Datasheet(PDF) 39 Page - Renesas Technology Corp

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