7549 datasheet(39/86 Pages) RENESAS

39 / 86 page

Rev.2.02

Mar 31, 2009

Page 37 of 81

REJ03B0202-0202

7549 Group

(2) Asynchronous Serial I/O (UART) Mode

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

clearing the serial I/O mode selection bit of the serial I/O control

Eight serial data transfer formats can be selected, and the transfer

formats used by a transmitter and receiver must be identical.

The transmit and receive shift registers each have a buffer, but

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

is written to the transmit buffer register, and receive data is read

from the receive buffer register.

The transmit buffer register can also hold the next data to be

transmitted, and the receive buffer register can hold a character

while the next character is being received.

Fig 47. Block diagram of UART serial I/O

Fig 48. Operation of UART serial I/O function

1/4

PE FE

1/16

Data bus

Receive buffer register

Address 001816

Receive shift register

Receive buffer full flag (RBF)

Receive interrupt request (RI)

Baud rate generator

Frequency division ratio 1/(n+1)

Address 001C16

ST/SP/PA generator

Transmit buffer register

Transmit shift register

Address 001816

Transmit shift completion flag (TSC)

Transmit buffer empty flag (TBE)

Transmit interrupt request (TI)

Address 001916

ST detector

SP detector

UART control register

Address 001B16

Character length selection bit

Address 001A16

BRG count source selection bit

Transmit interrupt source selection bit

Serial I/O1 synchronous clock selection bit

Clock control circuit

Character length selection bit

7 bits

8 bits

Serial I/O1 status register

Serial I/O 1 control register

P06/SCLK

P04/RXD

P05/TXD

φSOURCE

TSC=0

TBE=1

RBF=0

TBE=0

RBF=1

TBE=1

TSC=1*

Transmit or receive clock

Transmit buffer

write signal

Serial output TXD

Receive buffer

read signal

Serial input RXD

* 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 (s)

Notes 1: Error flag detection occurs at the same time that the RBF flag becomes “1” (at 1st stop bit, during reception).

2: As the transmit interrupt (TI), when either the TBE or TSC flag becomes “1”, can be selected to occur depending on the setting of the transmit

interrupt source selection bit (TIC) of the serial I/O1 control register.

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

4: After data is written to the transmit buffer when TSC=1, 0.5 to 1.5 cycles of the data shift cycle is necessary until changing to TSC=0.

7549 Datasheet(PDF) 39 Page - Renesas Technology Corp

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