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7721 Group User’s Manual

11–31

SERIAL I/O

11.4 Clock asynchronous serial I/O (UART) mode

Table 11.4.1 lists the performance overview in the UART mode, and Table 11.4.2 lists the functions of

I/O pins in this mode.

Table 11.4.1 Performance overview in UART mode

Item

Transfer data

format

Transfer rate

Error detection

Start bit

Character bit (Transfer data)

Parity bit

Stop bit

When selecting internal clock

When selecting external clock

Functions

1 bit

7 bits, 8 bits, or 9 bits

0 bit or 1 bit (Odd or even can be selected.)

1 bit or 2 bits

BRGi’s output divided by 16

Maximum 312.5 kbps

4 types (Overrun, Framing, Parity, and Summing)

Presence of error can be detected only by checking error sum flag.

Table 11.4.2 Functions of I/O pins in UART mode

Method of selection

(Cannot be used as a programmable I/O port even when

performing only reception.)

Port P8 direction registerU1’s corresponding bit = “0”

(Can be used as a programmable I/O port when performing

only transmission.)

Internal/External clock select bitU2 = “0”

Internal/External clock select bit = “1”

____ ____

CTS/RTS function select bitU3 = “0”

____ ____

CTS/RTS function select bit = “1”

Pin name

TxDi (P83, P87) (Note 1)

RxDi (P82, P86)

CLKi (P81, P85)

____ ____

CTSi

/RTSi (P80, P84)

(Note 2)

Functions

Serial data output

Serial data input

Programmable I/O port

BRGi’s count source input

____

CTS input

____

RTS output

Port P8 direction registerU1: address 1416

Internal/External clock select bitU2: bit 3 at addresses 3016, 3816

____ ____

CTS/RTS select bitU3: bit 2 at addresses 3416, 3C16

Notes 1: The TxDi pin outputs “H” level while transmission is not performed after selecting UARTi’s operating

mode.

____ ____

2: The CTSi/RTSi pin can be used as an input port when performing only reception and not using

___

the RTS function (when selecting CTS function).

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