JPH1093660A - Communication speed automatic deciding circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate the setting of a communication speed by a person and to efficiently transfer data by automatically deciding the optimum communication speed that is suitable for an input-output I/F cable length which connects inter-devices or inter-input-output devices of a communication controller. SOLUTION: When power is inputted to a communication controller 1, reference voltage is outputted from a reference voltage part 4 to a voltage detecting signal line 3, and voltage that moves around the line 3 one time brings about voltage drop due to direct current resistance. A voltage drop detecting part 5 compares the voltage that circulates the line 3 once with the reference voltage and calculates an input-output I/F cable length that connects the controller 1 and an input-output device 8 based on the value X which calculates a voltage drop amount of the line 3. A communication speed deciding part 6 instructs a clock generating part 7 to generate the clock of a communication speed that is decided based on the cable length. Thereby, the optimum communication speed is automatically decided in accordance with the cable length and data transfer is efficiently performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for automatically determining a communication speed of a communication control device, and more particularly to an automatic communication speed control device for automatically setting an optimum communication speed between communication control devices or between a communication control device and an input / output device. To do.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional configuration block. In the figure, 31 is a communication control device, 39a is a communication unit for exchanging data transfer with a communication unit 39b in the input / output device 38, and 37 is a communication unit for performing data transfer between the communication control device 31 and the input / output device 38. This is a clock generator for setting the communication speed. Reference numeral 36 denotes software for setting the clock cycle of the clock generator 37, that is, the communication speed by an operator.

[0003] Usually, the communication speed for data transfer is:
Even when the longest input / output interface cable is used to connect devices that perform data transfer, distortion of the transmission signal waveform and crosstalk (crosstalk) caused by the characteristic impedance and capacity of the input / output interface cable occur. It is decided not to.

That is, the conventional data transfer is performed within a range of the maximum cable length with a constant data communication speed between the communication control devices or between the communication control device and the input / output device.

[0005]

However, the input / output interface cable for connecting between the communication control devices or between the communication control device and the input / output device used in the prior art shown in FIG. 3 is shorter than the maximum cable length. Is used. For this reason, although the communication speed can be set higher than the communication speed according to the maximum cable length, the communication speed according to the maximum cable length is set and the inefficient data transfer is performed. was there. In addition, there is a problem that it is impossible to set a communication speed for efficiently performing data transfer without knowledge of data communication.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and is suitable for the length of an input / output interface cable connecting between communication control devices or between a communication control device and an input / output device. By automatically determining the optimum communication speed, the setting of the communication speed performed by the operator or the like becomes unnecessary, and efficient data transfer becomes possible.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a communication speed automatic determination circuit of a communication control device in which a communication control device or a communication control device and an input / output device are connected by an input / output interface cable, the communication control device automatically returns to the input / output interface cable at the end. A voltage detection signal line forming one loop is provided, and the communication control device detects a voltage drop caused by the reference voltage having passed through the voltage detection signal line, and a reference voltage section for outputting a reference voltage to the voltage detection signal line. A voltage drop detector that performs
By calculating the length of the input / output interface cable from the value of the voltage drop and determining the communication speed suitable for the length, the communication speed determination unit determines the maximum speed suitable for the length of the input / output interface cable. It is possible to efficiently perform data transfer at a high communication speed.

[0008]

FIG. 1 is a block diagram showing the configuration of the present invention. In the figure, reference numeral 1 denotes a communication control device. The communication control device 1 includes a communication unit 9a for exchanging data transfer with a communication unit 9b in the input / output device 8 and an input / output interface cable for calculating an input / output interface cable length. A loop-shaped voltage detection signal line 3 provided in the output interface cable, a reference voltage unit 4 for outputting a reference voltage to the voltage detection signal line 3, and a voltage generated when the reference voltage goes around the voltage detection signal line 3 A voltage drop detector 5 for detecting a value of the voltage drop, and a communication for calculating an input / output interface cable length based on the value of the voltage drop obtained by the voltage drop detector 5 and determining a highest communication speed suitable for the cable length. It comprises a speed determining unit 6 and a clock generating unit 7 for setting a communication speed for performing data transfer between the communication control device 1 and the input / output device 8. Reference numeral 2 denotes a block constituting a communication speed automatic determination circuit of the present invention.

FIG. 2 shows an example of a processing flowchart of the present invention. Hereinafter, the processing will be described according to this flow.

In step S201, when the power of the communication control device 1 is turned on, the voltage detection signal line 3
Outputs a reference voltage. The voltage that has passed through the voltage detection signal line 3 causes a voltage drop due to the DC resistance of the voltage detection signal line 3.

In step S202, the voltage drop detector 5 compares the voltage that has passed through the voltage detection signal line 3 with the reference voltage, and calculates the voltage drop of the voltage detection signal line 3.

In step S203, based on the voltage drop calculated in step S202, the cable length of the input / output interface cable connecting the communication control device 1 and the input / output device 8 is calculated by the voltage drop detecting unit 5. .

In step S204, the fastest communication speed suitable for the interface is determined by the voltage drop detecting section 5 based on the input / output interface cable length calculated in step S203.

In step S205, the communication speed determination unit 6 instructs the clock generation unit 7 to generate a clock having the communication speed determined in step S204.

[0015]

The present invention is embodied in the form described above, and has the following effects.

It is not necessary to set the communication speed between the communication control devices or between the communication control device and the input / output device. Further, since data transfer between the communication control device and the input / output device can be performed at an optimum communication speed, efficient data transfer can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of the present invention.

FIG. 2 is an example of a processing flowchart of the present invention.

FIG. 3 is a block diagram of a conventional configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Communication control device 3 Voltage detection signal line 4 Reference voltage part 5 Voltage drop detection part 6 Communication speed determination part 8 Input / output device

Claims (1)

[Claims] An automatic communication speed determining circuit for a communication control device, wherein the communication control device (1) or the communication control device (1) and the input / output device (8) are connected by an input / output interface cable. A voltage detection signal line (3) is formed in the interface cable at the end to form a loop, and the communication control device (1) is connected to a reference voltage unit (3) that outputs a reference voltage to the voltage detection signal line (3). 4) and a voltage drop detector (5) for detecting a voltage drop caused by the reference voltage having made a round of the voltage detection signal line (3).
And a communication speed determining unit (6) for calculating the length of the input / output interface cable based on the value of the voltage drop and determining a communication speed suitable for the length. .