7480 datasheet(237/337 Pages) RENESAS

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7480 Group and 7481 Group User's Manual

2-22

APPLICATIONS

2.3 Serial I/O

2.3.2 Application Example of Clock Asynchronous Serial I/O (UART) Reception

Processing of Received Data Bytes as a Packet

POINT: RAM area is secured by adding the several bytes to the maximum number of bytes necessary

for data processing, and the received data is stored in increasing order of address in the

interrupt service routine. If the data overflows the RAM area, the overflow data is stored at

the start address of the RAM.

When the received data whose byte number satisfies the requirement of data processing is

stored completely in the buffer area, the data processing is performed in the main routine.

As a result, the received data can be stored without losing any bits of data in process even

when the subsequent received data is stored completely during the data processing.

SPECIFICATIONS:

Clock: f(XIN) = 7.9872 MHz

UART reception

• Baud rate : 9600 bps

• Synchronous clock : f(XIN) is divided into 9.6 kHz

• Communication format: 1ST-8DATA-1SP

Processing received data as a packet

The head data of every packet consists of the code characteristic for the head

data and the code indicating the number of bytes of the packet.

Figure 2.3.5 shows a connection example.

Figure 2.3.6 shows the setting example of the

synchronous clock.

Figure 2.3.7 shows a communication format.

Figure 2.3.8 shows a control procedure example

of serial I/O receive.

Figure 2.3.7 Communication Format

Figure 2.3.6 Setting Example of Synchronous Clock

f(XIN) = 7.9872 MHz

BRG count source

selection bit

Baud rate

generator

Synchronous clock

9.6 kHz

Baud rate : 9600bps

1/4

1/13

1/16

Clock

generator

‘0’

‘1’

BRG output

Figure 2.3.5 Connection Example

TxD

P14/RxD

7480 Group

7481 Group

(Receiver)

Microcomputer

(Transmitter)

LSB

MSB

Transmit data (1ST-8DATA-1SP)

1st byte

(n – 1)th byte

1 packet (N bytes)

Head data

∗

ST:

Di:

SP:

Start bit

Data bit (i = 0 to 7)

Stop bit

The number of bytes of the packet

: Consists of the code characteristic for the head data

and the code indicating the number of bytes of

the packet.

∗

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