7480 datasheet(239/337 Pages) RENESAS

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7480 Group and 7481 Group User's Manual

2-24

APPLICATIONS

2.3 Serial I/O

2.3.3 Application Example of Bus Arbitration Interrupt

LAN Communications in Contention Bus System

POINT: In LAN communications with the contention bus system, the malfunction of transmission due

to bus collision is detected with a bus arbitration interrupt.

SPECIFICATIONS:

Clock: f(XIN) = 7.9872 MHz

LAN communication format: Simplified SAE J1850 (PWM system)

The CNTR0 pin is connected to the RxD pin, and SOF is detected with the

rising edge of a CNTR0 pin input

Data is transmitted and received by clock synchronous serial I/O communications.

• Baud rate: 41600 bps

• Synchronous clock: f(XIN) is divided into 41.6 kHz

• Bus collision detected

The HIGH level has priority on LAN communication line at bus collision

Figure 2.3.9 shows a connection example.

Figure 2.3.10 shows a setting example of the synchronous clock.

Figure 2.3.11 shows a communication format example of simple SAE J1850.

Figure 2.3.12 shows a communication timing example.

Figures 2.3.13 and 2.3.14 show control procedure examples.

P14/RxD

P15/TxD

7480 Group

7481 Group

P40/CNTR0

OUT

BUS +

BUS –

Driver

LAN communication Line (+)

LAN communication Line (–)

Unit A

Unit B

Unit C

Unit D

Unit A

TxD pin output

Unit B

TxD pin output

LAN communication line

(RxD pin input)

• Conflicts between unit A and unit B

Bus collision

detected in unit B

Figure 2.3.9 Connection Example

Baud rate : 41600bps

f(XIN)=7.9872MHz

1/4

1/3

1/4

BRG count source

selection bit

Baud rate

generator

Synchronous clock

41.6 kHz

Clock

generator

‘0’

‘1’

BRG output

Figure 2.3.10 Setting Example of Synchronous Clock

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