JPH0457142B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a data communication system belonging to a local network interconnecting computer equipment distributed over a relatively small area.

<<Background of the Invention>> Recently, small-scale networks that interconnect computer equipment located within the same building, factory, or site, ie, local networks, have been actively developed. Most of the various local networks currently known are based on baseband transmission, and there are very few carrier-type networks. Some transport-type systems have a carrier on/off at the transport terminal.
Since the carrier of the receiving line is turned on and off according to the switching off, the PSK (phase shift keying) method, which requires synchronization due to problems such as the relatively long carrier stabilization time at the receiving terminal, is not used. , mainly used the FSK (Frequency Shift Keying) method. As a result, each terminal cannot be synchronized, and the carrier and collision detection process for CSMA/CD (carrier sense mass access/collision detection) control becomes long, resulting in lower efficiency than baseband transmission. .

<<Object of the Invention>> The object of the invention is to connect a plurality of communication stations to a bus with a head-end device at one end, and to transmit data frames using the two-phase PSK modulation method and HDLC (High Level Data Link) procedure between these communication stations. format,
A system that performs data communication using the CSMA/CD access method.In particular, the bus is of a frequency multiplexing center split type, all communication stations are always synchronized with the reference carrier wave of the head-end device, and each communication station is
The playback stabilization time of the synchronous carrier wave for PSK demodulation is short,
Another object of the present invention is to provide a data communication system in which the detection process of CSMA/CD control is shortened.

<<Configuration and Effects of the Invention>> In order to achieve the above object, in the data communication system according to the present invention, the head end device receives a clock signal of frequency 1, a reference carrier wave of frequency 2 which is an integer multiple of 1, and an integer number of 3. means for generating a reference carrier wave with a frequency of 3, and a reception/demodulation unit that receives a two-phase PSK signal of a frequency of 2 output from the communication station to the bus and demodulates it using the reference carrier wave 2 and the clock signal 1. When there is no received signal in this reception/demodulation procedure, the data string obtained by actively encoding a series of "1" data is used as modulation data, and when there is the above received signal, the demodulated output thereof is used as modulation data, and the above The communication station has modulation/transmission means for creating two-phase PSK at frequency 3 using reference carrier wave 3 and outputting it to the bus;
a receiving means for receiving a two-phase PSK signal, and a clock signal 1 and a reference carrier wave 2 from the output of this receiving means.
and 3, as well as demodulating the received output, and a reproducing/demodulating means for demodulating the received output, using the operationally encoded transmission data as modulation data, and using the regenerated clock signal 1 and the reference carrier wave 2 to generate a two-phase signal with a frequency of 2.
Based on the modulation/transmission means that creates a PSK signal and outputs it to the above bus, and the output of the above playback/demodulation means.
The present invention is characterized by comprising means for performing CSMA/CD type access control.

According to this system, all communication stations can be kept in synchronization with the reference carrier wave from the head-end equipment at all times, and the start-up of PSK demodulation operation at each communication station is extremely good, and the start-up of CSMA/CD control is also improved. Improved performance and efficient data communication.

<<Description of Embodiments>> FIG. 1 shows the overall configuration of this system.
A head end device HE is provided at one end of the bus 1, and a large number of communication stations T1 to Tn are connected to the bus 1. Frequency 3 from headend device HE to bus 1
A two-phase PSK signal is constantly output, and each communication station T1 to Tn receives this.

The communication station Ti (i=1 to n) outputs transmission data in the data frame format of the HDLC procedure to the bus 1 in the form of a two-phase PSK signal of frequency 2, in accordance with the access control of CSMA/CD. The head end device HE receives this signal, demodulates it, and outputs it to the bus 1 again in the form of a two-phase PSK signal using a carrier wave of frequency 3.

The communication station Ti that sent the received data compares the data it sent with the data sent back to the bus 1 from the head end device HE in the form of a two-phase PSK signal of frequency 3 to detect a collision.

Also, the data sent from a certain transmitting station Ti is
2-phase PSK with frequency 3 from headend equipment HE
It is received in the form of a signal by all other communication stations T1-Tn. Each communication station T1 to Tn reads the target address written in the received frame, and if the address matches its own address, it reads the subsequent data. Then, if there is no error as a result of the CRC check, an ACK frame is sent to the transmitting station.

FIG. 2 shows the configuration of the head end device HE. In the head end device HE, the reference oscillator 2
By dividing the output of by frequency divider 3, the frequency
A clock signal of 1, a reference carrier wave of frequency 2 which is an integer multiple of 1, and a reference carrier wave of frequency 3 which is an integer ratio of 2 are generated. Below, these signals are referred to as clock signal 1,
They are written as reference carrier wave 2 and reference carrier wave 3.

A two-phase PSK signal of frequency 2 output from the communication station Ti to the bus 1 is received by a receiving circuit 4 consisting of a bandpass filter and an automatic gain control type amplifier in the head end device HE, and is input to a demodulating circuit 5.
The receiving circuit 4 outputs a carrier detection signal CD indicating whether or not a carrier of frequency 2 is present on the bus 1, and supplies this to the modulation circuit 6.

The demodulation circuit 5 receives the clock signal 1 from the frequency divider 3.
The output of the receiving circuit 4 is demodulated using the reference carrier wave 2 and the demodulated data RSD. This demodulated data
RSD becomes the modulation input of the modulation circuit 6.

The modulation circuit 6 is a two-phase signal with a frequency of 2 in the receiving circuit 4.
When a PSK signal is being received (carrier detection signal CD is output), the demodulated output RSD of the demodulation circuit 5 is used as modulation data, the clock signal 1 of the frequency divider 3 and the reference carrier wave 3 are used, and the data RSD
Create a two-phase PSK signal with frequency 3 modulated by
This signal is output to the bus 1 by a transmitter circuit 7 consisting of an amplifier and a bandpass filter. In other words, the two-phase PSK signal of frequency 2 output from the communication station T1 is transmitted to the head end device HE by the two-phase PSK signal of frequency 3.
The frequency is converted to a PSK signal and output to bus 1 again.

Furthermore, when the carrier of frequency 2 is not outputted from any of the communication stations T1 to Tn and the carrier detection signal CD of the receiving circuit 4 is not outputted, the modulation circuit 6 operates as follows. At this time, the modulation circuit 6
uses a data string obtained by differentially encoding a series of "1" data as modulation data, and uses the above clock signal 1 and reference carrier wave 3 to generate a two-phase PSK signal with a frequency of 3.
A signal is generated and outputted to the bus 1 via the transmission circuit 7. In other words, when none of the communication stations T1 to Tn are transmitting, the head end device HE always sends data at frequency 3, which is modulated with a data string obtained by differentially encoding a series of "1" data.
A phase PSK signal is output on bus 1. Each communication station T1 to Tn receives this signal, and from the received signal clock signal 1, reference carrier wave 2, reference carrier wave
Play 3. For this reason, each communication station T1 to Tn is always kept in a synchronized state by the head end device HE.

FIG. 3 shows the configuration of one communication station Ti.
The two-phase PSK signal of frequency 3 output from the head end device HE to bus 1 is sent to the communication station Ti.
The signal is received by a receiving circuit 8 consisting of a bandpass filter and an automatic gain control type amplifier. The output of the receiving circuit 8 is input to a reference signal reproducing circuit 9, and this circuit constitutes a clock signal 1, a reference carrier wave 2, and a reference carrier wave 3.

The demodulation circuit 10 demodulates the output of the reception circuit 8 using the reproduced clock signal 1 and reference carrier wave 3 to obtain reception data RD. Access control section 15
is the received data RD input from the demodulation circuit 10
If this data is a data string obtained by differentially encoding a series of "1" data, it is recognized that the carrier of frequency 2 is not output from any of the communication stations T1 to Tn on bus 1. do. In other words, it is recognized that bus 1 is not in use.

Note that the receiving circuit 8 receives a carrier detection signal CD indicating whether or not a carrier of frequency 3 exists on the bus 1.
is output and given to the access control unit 15.
The access control unit 15 is normal when the carrier detection signal CD is input, and recognizes that some abnormality has occurred in the system when the signal CD disappears.

When there is data to be transmitted, the access control unit 15 recognizes that the bus 1 is not in use as described above and transmits the differentially encoded transmission data.
SD is given to the modulation circuit 11. The modulation circuit 11 is
Using the recovered clock signal 1 and reference carrier wave 2, a two-phase signal with frequency 2 modulated by the transmitted data SD
Create PSK signal. This signal is output to the bus 1 by a transmitting circuit 12 consisting of an amplifier and a bandpass filter.

When a 1-phase PSK signal of frequency 2 modulated with the data SD is output from the communication station Ti in this way, a 2-phase PSK signal of frequency 3 modulated with the transmission data SD is output by the action of the head end device HE described above.
The PSK signal is sent back to bus 1. This signal is received by the receiving circuit 8 of the communication station Ti, and the demodulating circuit 10
It is demodulated by At this time, the demodulated data RD has the same content as the transmitted data S with a delay of two clocks. Therefore, in the communication station Ti that performed the transmission, the transmitted data SD is transferred to the shift register 13 using the regenerated clock signal 2.
The EOR circuit 14 compares the delayed data with the received data RD output from the demodulation circuit 10. If both input data of the EOR circuit 14 match, its output DS is "0", indicating that no collision has occurred. When transmission is performed simultaneously from multiple communication stations, the EOR circuit 14 is activated at each transmitting station.
Both input data do not match, and the output DS is “1”
becomes. The access control unit 15 receives DS="1" and recognizes that a collision has occurred. After this, retransmission operations are performed in accordance with the well-known CSMA/CD control procedure.

Note that bus 1 may use a dedicated transmission line such as a coaxial cable, but by taking advantage of the carrier type,
The power supply wiring may be used as the bus 1. In that case, the wiring cost of the transmission line will be poor and the configuration will be optimal for a simple local network.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of the entire system, FIG. 2 is a diagram showing the configuration of a head end device HE, and FIG. 3 is a diagram showing the configuration of one communication station Ti. HE...Head end device, T1-Tn...Communication station, 1...Bus, 2...Reference oscillator, 3...Frequency divider, 4...Receiving circuit, 5...Demodulation circuit, 6...Modulation circuit, 7... Transmission circuit, 8... Receiving circuit, 9...
...Reference signal regeneration circuit, 10...Demodulation circuit, 11...
... Modulation circuit, 12 ... Transmission circuit, 13 ... Shift register, 14 ... EOR circuit, 15 ... Access control section.

Claims (1)

[Claims] 1. A plurality of communication stations are connected to a bus provided with a head-end device at one end, and two-phase PSK is established between these communication stations.
Modulation method, data frame format of HDLC procedure,
This is a system that performs data communication using the CSMA/CD access method.
means for generating a clock signal of 1, a reference carrier wave of frequency 2 which is an integer multiple of 1, a reference carrier wave of frequency 3 which is an integer ratio of 2, and a two-phase PSK signal of frequency 2 output from the communication station to the bus. A reception/demodulation procedure for receiving and demodulating using the reference carrier wave 2 and clock signal 1, and a data string obtained by differentially encoding a series of "1" data when there is no reception signal of this reception/demodulation means. When there is the above received signal, the demodulated output is used as the modulated data, and the two-phase signal of frequency 3 is generated using the above reference carrier wave 3.
The communication station has a modulation/transmission means for generating a PSK signal and outputting it to the bus; regenerating/demodulating means for regenerating the clock signal 1, reference carrier waves 2 and 3 from the output of the clock signal, and demodulating the received output;
The actuation-encoded transmission data is used as modulation data,
Regenerated clock signal 1 and reference carrier wave above
2 to create a two-phase PSK signal of frequency 2 and output it to the above bus, and the above playback/transmission means.
A data communication system comprising: means for performing CSMA/CD access control based on the output of the demodulating means.