Communication system, communication device and method for determining duty ratio of PWM control

Abstract

A communication system includes: a master; a plurality of slaves; and a bus for coupling among the master and the plurality of slaves in order to communicate asynchronously among the master and the plurality of slaves. The master supplies electricity to the bus in a power supply period. The master or the slave drives the bus for transmitting a one-bit data through the bus in a data transmission period. The power supply period and the data transmission period are successively performed so that data communication provided by a plurality of one-bit periods is performed among the master and the plurality of slaves. The master finely changes a communication frequency in the data communication. The master changes a drive level of the bus within a predetermined acceptable range in the data communication.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a circuit diagram showing a master in a communication system with using a SbW method according to a first embodiment;

FIG. 2 is a circuit diagram showing a frequency dispersion element in a voltage driver of the master;

FIG. 3A is a table showing a relationship between a variation of communication bit rate and a load data, and FIG. 3B is a chart showing a state transition condition;

FIG. 4A to 4D are graphs showing a timing chart of operation of the frequency dispersion element;

FIG. 5 is a circuit diagram showing a driving voltage/current control element in the voltage driver;

FIG. 6 is a circuit diagram showing a slave in the communication system;

FIG. 7 is a circuit diagram showing a construction for driving a bus with a level “VL1” or “VLS0” in the driver/receiver;

FIG. 8 is a graph showing a voltage waveform when the master or the slave drives the bus;

FIG. 9A to 9C are charts showing a method for changing a bit rate finely, according to a second embodiment;

FIG. 10 is a circuit diagram showing a construction for controlling and changing the bit rate;

FIG. 11 is a flow chart showing a process in a variation control portion;

FIG. 12 is a circuit diagram showing a driving control device for controlling and driving a motor on a vehicle;

FIG. 13 is a chart showing a process for exchanging information between a control IC and a database;

FIG. 14 is a circuit diagram showing a communication system according to a related art;

FIG. 15 is a graph showing a voltage waveform when a master or a slave drives a bus in the system; and

FIGS. 16A and 16B are charts showing a data communication between the master and the slave.

Claims

1. A communication system comprising: a master;a plurality of slaves; anda bus for coupling among the master and the plurality of slaves in order to communicate asynchronously among the master and the plurality of slaves, whereinthe master supplies electricity to the bus in a power supply period, the master or the slave drives the bus for transmitting a one-bit data through the bus in a data transmission period, the power supply period and the data transmission period are successively performed so that data communication provided by a plurality of one-bit periods is performed among the master and the plurality of slaves,the master finely changes a communication frequency in the data communication, andthe master changes a drive level of the bus within a predetermined acceptable range in the data communication.

2. The system according to claim 1, wherein the master changes a time for a level transition when the master drives the bus.

3. The system according to claim 2, wherein the master changes a current driving performance when the master drives the bus.

4. The system according to claim 1, wherein the master determines a variation of a transmission time in a communication frame within a predetermined acceptable range,the communication frame includes a plurality of one-bit data,each one-bit data is transmitted in a one-bit period having a transmission time, andthe transmission time of each one-bit data is changeable in such a manner that a total variation of the transmission times of the plurality of one-bit data is within the variation of transmission time in the communication frame.

5. The system according to claim 1, wherein the master changes the communication frequency with a cyclic pattern.

6. The system according to claim 1, wherein the slave changes a drive level of the bus within a predetermined acceptable range in the data communication.

7. The system according to claim 1, wherein the slave changes a time for a level transition when the slave drives the bus.

8. The system according to claim 7, wherein the slave changes a current driving performance when the slave drives the bus.

9. A communication device used for the communication system according to claim 1, wherein the communication device provides the master.

10. A communication device used for the communication system according to claim 6, wherein the communication device provides the slave.

11. A communication system comprising: a master;a plurality of slaves; anda bus for coupling among the master and the plurality of slaves in order to communicate asynchronously among the master and the plurality of slaves, whereinthe master supplies electricity to the bus in a power supply period,the master or the slave drives the bus for transmitting a one-bit data through the bus in a data transmission period,the power supply period and the data transmission period are successively performed so that data communication provided by a plurality of one-bit periods is performed among the master and the plurality of slaves,the master finely changes a communication frequency in the data communication, andthe master changes a time for a level transition when the master drives the bus.

12. The system according to claim 11, wherein the master changes a current driving performance when the master drives the bus.

13. The system according to claim 11, wherein the master determines a variation of a transmission time in a communication frame within a predetermined acceptable range,the communication frame includes a plurality of one-bit data,each one-bit data is transmitted in a one-bit period having a transmission time, andthe transmission time of each one-bit data is changeable in such a manner that a total variation of the transmission times of the plurality of one-bit data is within the variation of transmission time in the communication frame.

14. The system according to claim 11, wherein the master changes the communication frequency with a cyclic pattern.

15. The system according to claim 11 wherein the slave changes a drive level of the bus within a predetermined acceptable range in the data communication.

16. The system according to claim 11 wherein the slave changes a time for a level transition when the slave drives the bus.

17. The system according to claim 16, wherein the slave changes a current driving performance when the slave drives the bus.

18. A method for determining a duty ratio of a PWM control comprising: outputting a PWM signal to a driving circuit so that switching of a load is controlled;determining a duty ratio target value of the PWM signal;changing the duty ratio of the PWM signal around the duty ratio target value as a center of a variation in such a manner that an average of the variation of the duty ratio in a predetermined period coincides with the duty ratio target value;measuring a noise level when the PWM signal is outputted to the driving circuit;memorizing a data of the noise level together with the variation of the duty ratio in the changing the duty ratio; anddetermining the variation of the duty ratio based on the data of the noise level when an operational environment or an operational condition are given so that the noise level in a given frequency range as a reduction object is reduced.