7516 datasheet(24/90 Pages) RENESAS

24 / 90 page

Rev.1.01

Jul 01, 2003

page 24 of 89

7516 Group

Fig. 21 Operation of UART serial I/O1 function

[Transmit Buffer Register/Receive Buffer

The transmit buffer register and the receive buffer register are lo-

cated at the same address. The transmit buffer is write-only and

the receive buffer is read-only. If a character bit length is 7 bits, the

MSB of data stored in the receive buffer is “0”.

[Serial I/O1 Status Register (SIOSTS)] 001916

The read-only serial I/O1 status register consists of seven flags

(bits 0 to 6) which indicate the operating status of the serial I/O1

function and various errors.

Three of the flags (bits 4 to 6) are valid only in UART mode.

The receive buffer full flag (bit 1) is cleared to “0” when the receive

buffer register is read.

If there is an error, it is detected at the same time that data is

transferred from the receive shift register to the receive buffer reg-

ister, and the receive buffer full flag is set. A write to the serial I/O1

status register clears all the error flags OE, PE, FE, and SE (bit 3

to bit 6, respectively). Writing “0” to the serial I/O1 enable bit SIOE

(bit 7 of the serial I/O1 control register) also clears all the status

flags, including the error flags.

Bits 0 to 6 of the serial I/O1 status register are initialized to “0” at

reset, but if the transmit enable bit (bit 4) of the serial I/O1 control

2) and the transmit buffer empty flag (bit 0) become “1”.

[Serial I/O1 Control Register (SIOCON)] 001A16

The serial I/O1 control register consists of eight control bits for the

serial I/O1 function.

[UART Control Register (UARTCON)] 001B16

The UART control register consists of four control bits (bits 0 to 3)

which are valid when asynchronous serial I/O is selected and set

the data format of an data transfer and one bit (bit 4) which is al-

ways valid and sets the output structure of the P25/TXD pin.

[Baud Rate Generator (BRG)] 001C16

The baud rate generator determines the baud rate for serial trans-

fer.

The baud rate generator divides the frequency of the count source

by 1/(n + 1), where n is the value written to the baud rate genera-

tor.

TSC=0

TBE=1

RBF=0

TBE=0

RBF=1

TBE=1

TSC=1

Transmit or receive clock

Transmit buffer write

signal

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)

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.

Notes

Serial output TXD

Serial input RXD

Receive buffer read

signal

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