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SERIAL I/O

7721 Group User’s Manual

11–6

11.2 Block description

11.2.2 UARTi transmit/receive control register 0

Figure 11.2.3 shows the structure of UARTi transmit/receive control register 0. For bits 0 and 1, refer to

section “11.2.1 (1) Internal/External clock select bit (bit 3).”

Fig. 11.2.3 Structure of UARTi transmit/receive control register 0

(1)

____ ____

CTS/RTS select bit (bit 2)

____

By clearing this bit to “0” in order to select the CTS function, pins P80 and P84 function as CTS input

pins, and the input signal of “L” level to these pins becomes one of the transmission conditions.

____

By setting this bit to “1” in order to select the RTS function, pins P80 and P84 become RTS output

____

pins. When the receive enable bit (bit 2 at addresses 3516, 3D16) is “0” (reception disabled), the RTS

output pin outputs “H” level.

____

In the clock synchronous serial I/O mode, the output level of the RTS pin becomes “L” when reception

conditions are satisfied, and it becomes “H” when reception starts. Note that, when an internal clock

____

is selected (bit 3 at addresses 3016, 3816 = “0”), the RTS output is undefined. Accordingly, do not

____

select the RTS function.

____

In the clock asynchronous serial I/O mode, the output level of the RTS pin becomes “L” when the

receive enable bit is set to “1.” It becomes “H” when reception starts and it becomes “L” when

reception is completed.

(2)

Transmit register empty flag (bit 3)

This flag is cleared to “0” when the UARTi transmit buffer register’s contents are transferred to the

UARTi transmit register. When transmission is completed and the UARTi transmit register becomes

empty, this flag is set to “1.”

CTS/RTS select bit

Bit

BRG count source select bits

Bit name

At reset

Functions

0 0 : f2

0 1 : f16

1 0 : f64

1 1 : f512

UART0 transmit/receive control register 0 (Address 3416)

UART1 transmit/receive control register 0 (Address 3C16)

b1 b0

0 : CTS function selected

1 : RTS function selected

Transmit register empty flag

0 : Data present in transmit register

(During transmission)

1 : No data present in transmit register

(Transmission completed)

7 to 4

Nothing is assigned.

Undefined

–

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