JPS5841704B2 - Daiko-dofugoudensouhoushiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides data transmission based on an asynchronous method in which a start pulse and a stop pulse are inserted before and after the text to be transmitted between a transmitting side and a receiving side that are in an asynchronous relationship. This relates to the transmission method used for transmission.

In conventional data transmission, modulation methods such as frequency modulation or phase modulation have often been used.

This modulation method has (1) a relatively narrow frequency bandwidth, and (2) no direct current component.

(3) Strong against noise.

It has the following advantages.

On the other hand, the frequency on the transmission path becomes higher than the transmission speed.

High frequencies on the transmission line have the disadvantage of increasing attenuation in the line.

Furthermore, recently, PCM transmission using a double-current method has been used as a data transmission method.

The PCM transmission method uses the above modulation methods (1), (2),
It is said to be an excellent method that satisfies the condition (3) and theoretically has the highest information transmission ability.

Therefore, it is conceivable to apply PCM codes without using frequency modulation or phase modulation even in data transmission using an asynchronous start-stop synchronization method.

However, although PCM codes can be easily created if PCM encoding is intended from the beginning, the circuit configuration becomes complicated when NRZ signals generated asynchronously are PCM encoded.

On the other hand, a dicode code is a code that can have the same properties as a PCM code using a double-current system.

With this dicode code, it is extremely easy to encode NRZ signals that occur asynchronously, but when applied to data transmission using the asynchronous method, it is difficult to take sufficient measures against malfunctions caused by noise. For this reason, despite the advantages mentioned above, data transmission using dicode codes has not been put into much practical use.

An object of the present invention is to provide a dicode code transmission system that can effectively prevent malfunctions due to noise.

In the start-stop synchronization method, as shown in FIG. 1a, the end of a character is a stop bit "1" and the beginning of a character is a start bit "0".

Synchronization is achieved by this change from "l" to "0".

In the dicode encoding transmission method, a bipolar method uses a single-current waveform in which the potential becomes negative only when there is a change from "0" to "1" or from "1" to "0", and zero potential when there is no change. The converted data is transmitted.

Therefore, the single-current waveform shown in Figure 1a has a negative pulse at the front end of the data part and a positive pulse at the rear end, as shown in Figure 1, if the data part is omitted in sections for simplicity. It becomes a waveform.

Here, if a stop bit "1" continues between a certain text and the following text, and noise occurs during this time and is mistakenly received as a negative pulse, the stop bit will be inverted.

That is, instantaneous noise may result in a long-term error, and data transmission using dicode codes has the property of being weak against noise.

According to this invention, malfunctions due to noise between adjacent texts can be effectively prevented.

That is, as shown in FIG. 2, one positive pulse is sent as a reset pulse prior to the transmission of each text.

Also in FIG. 2, the dicode-encoded data portion is omitted.

This reset pulse acts to ensure that the state of the receiver is set to ``1'' before receiving the text, even if the state of the receiver has been toggled to ``0'' by noise, thereby causing the state of the receiver to is received normally and without error.

Note that this reset pulse only needs to be sent out within a time that is not much longer than the start of text transmission, and its width does not necessarily have to be the same as the pulse width of the dicode code.

FIG. 3 shows a circuit configuration on the transmitting side when transmission is performed according to the method of the present invention.

Data to be transmitted is created by a data generation source 1 and supplied to a transmitter 2 as parallel signals in character units.

The transmitter 2 converts the received parallel signal into serial,
One text is created along with necessary signals such as a start bit, a stop bit, and an error control signal according to the normal start-stop synchronization method, and is sent to the encoding circuit 3.

Further, the data generation source 1 generates a reset pulse at the same time as sending out the first character, and this reset pulse is sent to the transmission line L1 for positive pulses via the OR gate 4.

Since there is a delay depending on the signal processing within the transmitter 2,
A reset pulse will be sent just before the start bit.

The encoding circuit 3 changes the level of the single-current waveform serial signal received from the transmitter 2 from "1" to "0" or from "0" to "1".
'' is encoded by generating a pulse only when there is a change in ``.'' The single-current encoded output is converted by a normal bipolar conversion circuit (not shown), resulting in the conversion shown in Figure 2. It becomes a dicode code like this.

That is, the encoding circuit 3 has a shift register 5 that operates to give a predetermined delay to the signal from the transmitter 2,
From this shift register 5, an output A generated at a timing determined by a clock pulse and an output B having a predetermined delay amount with respect to this output A are taken out.

Of these, the output A is directly sent to the first AND gate 6.
It is also supplied to the second AND gate 7 via an inverter 8.

The output B is then directly guided to the second AND gate I and to the first AND gate 6 via the inverter 9.

Therefore, the output terminal of the first AND gate 6 has an output A
is "H" and the level of output B is "H" only during rLl, and at the output terminal of the second AND gate 7, the level to the output is ILJ and the level of output B is "H" only during rLl.
A signal appears such that the level of is at rHJ level only during rHJ.

Note that the output of the AND gate 6 is sent to the outside via the aforementioned OR gate 4.

An example of the signal waveform of each part is shown in FIG.

Note that malfunctions due to noise in the dicode code occur not only during consecutive periods of stop bits to which the present invention is applied;
It also occurs in the middle of text.

If an error occurs in the middle of the text, there is a high probability that it will be a burst error due to the nature of the dicode code.

However, this problem can be solved by applying a known method such as double transmission verification.

As explained above, according to the present invention, a reset pulse is sent out prior to sending the text to forcibly reset the state of the receiving side, making it possible to reliably prevent transmission errors caused by noise. , making it possible to put transmission using dicode codes into practical use.

[Brief explanation of drawings]

1A and 1B are graphs showing an example of a signal format based on the normal asynchronous method, FIG. 2 is a graph showing an example of a signal format based on the method of the present invention, and FIG. 3 is a graph showing an example of the signal format based on the method of the present invention. Figure 4 is a block diagram showing the structure of the transmitting side when transmission is performed according to Figure 3.
It is a graph which shows the signal waveform of each part of a figure. 3... Encoding circuit, 4... OR gate, 6°... AND gate, 8, 9...
inverter.

Claims (1)

[Claims] 1. In data transmission using the asynchronous start-stop synchronization method, the transmitted data is dicode encoded, a start bit and a stop bit with different signs are inserted at the front and rear ends of the text, and a , a dicode code transmission system characterized in that a reset pulse having the same code as the stop bit is sent from the transmitting side, and then the text is transmitted.