JPH0129466B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a data transmission system using a communication line formed by connecting a plurality of lines in tandem.

Prior Art and Problems In some data transmission systems, as shown in FIG. 1, the communication line connecting the sending and receiving ends is made up of a plurality of lines connected in tandem. In this figure, 10 is a processing device such as a central CPU, 12 is a terminal device, and communication is performed between these devices. 14,16
is a communication line (telephone line) connecting the sending and receiving ends 10 and 12, and in this example, 14 is a time division multiplex communication line, and 16 is a time division multiplex communication line.
is a normal communication line. Connected before and after the line 14 are a transmission device 18 that time-division multiplexes signals from multiple lines into one line, and a transmission device 20 that returns the time-division multiplexed signals to individual line signals. Modems 22 and 24 are connected. Communication is normally carried out over a single line, such as only line 14 or only line 16, but as in the illustrated example, multiple lines may be used in tandem, such as by a modem (modulator/demodulator) or TDM (time division multiplexer). pairs may be connected in tandem.

To communicate through one line, for example, the line 16 to which modems 22 and 24 are connected, as shown in FIG.
When the permission signal CS is returned after a certain period of time τ from 2, the sending side receives the permission signal and transmits the data while CS is on.
Send SD. The fixed time τ is used to synchronize modems and prepare for transmission. The receiving side receives the transmitted data SD as the received data RD, but this reception is performed on the condition that the carrier detect CD sent before the RD is on.

Communication through one line 16 is as described above, but when line 14 is added to this, transmission device 20
is a receiving end when viewed from the line 14, and a transmitting end when viewed from the line 16 (assuming that communication is from the processing device 10 to the terminal device 12).Therefore, the transmission device 20 receives data transmitted from the processing device 10 and transmits the data. When sending to the terminal device 12, first raise the RS (this is
(generated by CD), when CS is returned from modem 22
RD will be sent as SD. Also, when the modem 22 receives an RS (this is received as an RS from the actual transmitting end), it cannot distinguish between the RS raised by the processing device 10 and the RS raised by the transmission device 20, so it uniformly sends a transmission request. received as RS),
CS will be turned on after a certain period of time.

However, since the transmission device 20 only performs relay transmission and is not a true transmitting end, RDs arrive one after another, and there is no time to wait for the CS and send it out.
A buffer is required to wait for the CS and then send the RD, but the transmission device 20 is not provided with a buffer. Therefore, the transmission device 20 transmits RD without waiting for CS.
It is designed to be sent immediately after receiving it. That is, the transmission device 20 is designed to be versatile in that it can be connected to a modem or directly connected to a terminal device. FIG. 3 shows the configuration of main parts of the transmission device 18, and FIG. 4 shows the structure of main parts of the transmission device 20 and modem 22.
The modem 22 is equipped with a delay circuit D, and delays RS by a time τ and sends CS. Also, transmission device 1
8, if an SD is present when RS is included, the communication data/control signal transmitter TR sends out the SD; this is also the case with the modem 22, although not shown. The transmission device 20 serving as a relay transmission end is equipped with a communication data/control signal receiving unit REC, receives SD and RS from the transmission device 18 on the transmission side, outputs RD and CD, and outputs RD and CD to the modem 2.
In 2, these are connected via an interface cable.
Receive as SD, RS. The modem 22 outputs the CS after a delay τ, but for the reason mentioned above, this CS is not used and is left alone. Therefore, data may be sent even though the modem 22 does not raise the permission signal CS, and the data before CS is not taken in, resulting in data loss.

To prevent this data loss, the time between RS and CS is τ
The processing device 10, which is the transmission source, must send data with sufficient consideration given to the following. Another problem with tandem-connected lines is that the time from when RS goes up to when CD turns on is not constant. That is,
CD occurs when the transmission equipment samples RS and detects that RS is turned on, but since the sampling clocks are asynchronous, any sampling clock
Discrepancies occur depending on whether RS ON can be detected. R.S.
This deviation is relatively large because the sampling clock of the control signal, such as , has a longer period than the data sampling clock. The time difference that the transmission source must take into consideration is the above-mentioned time τ plus this difference, and the time required for transmission (waiting time) becomes increasingly large. If we consider the case where multiple lines are connected in tandem, this time becomes even longer.

The transmission device 20 has a buffer, and after receiving the CS from the modem 22, the transmission device 20 receives the received data.
The above problem can be solved by sending RD. However, the number of connector pins of the transmission device 20 is 25.
It is determined by the standard that there are pins, etc., and there is no pin that takes in CS. Although it is relatively easy to provide a buffer, it is not easy to change the number of pins to achieve non-standard specifications.

OBJECTS OF THE INVENTION The present invention aims to improve the above points and provide a data transmission device system that does not require any changes to connectors or the like and does not cause data loss.

Structure of the Invention The present invention provides a tandem communication line that has a transmission device that performs time division multiplexing, a transmission device that returns the time division multiplexed signals to individual line signals at both ends, and a communication line that has a modem at both ends. In the connected data transmission system, the transmission device serving as one receiving end and the other transmitting end of the communication line has a buffer for storing received data, and a buffer between a transmission request signal and a permission signal in response to a carrier detection signal. The present invention is characterized in that it is provided with a timer that generates a signal instructing the buffer to send data after a time difference, and this will be explained next with reference to the embodiment shown in FIG.

Embodiment of the Invention In FIG. 5, the same parts as in FIG. 4 are given the same reference numerals, and 20 and 22 are the aforementioned transmission device and modem. In the present invention, the transmission device 20 has a FIFO
The difference from FIG. 4 is that a (First In First Out) type buffer B and timer T are provided. Timer T
instructs buffer B to start outputting after a certain period of time after receiving carrier detect signal CD. The delay time of timer T is the same as that of delay circuit D.
Therefore, equivalently, the permission signal generated by the modem 22
It is the same as inputting CS to buffer B, sending,
Like the transmitting end of a communication system where the receiving end is connected with a single line, data can be sent after the CS is returned. When using CS, the CS must be wired between the modem 22 and the transmission device 20, so the connector has a special specification with one more pin, but a timer equivalent to delay circuit D of the modem 22 is required. If T is provided in the transmission device 20, the connector may be of standard specification.

In the conventional method, the time setting that was required only in the transmission device 18 on the transmitting side is also required in the transmitting device 20 on the receiving side (relay transmitting side) in the method of the present invention, and the transmission device 20 also requires a buffer, which is a disadvantage. However, even when lines are connected in tandem, the difference in data transmission timing is just the delay τ between RS and CS, so there is no need to increase the waiting time, and there is no problem such as missing part of the data. Multiple connections can be made in any number of stages, and are very effective.

FIG. 6 shows transmission devices 18 and 2 to which the present invention is applied.
0 configuration is shown. As in all figures, parts that are the same as in other figures are given the same reference numerals. As is clear from the comparison, FIG. 6 shows the transmitting side shown in FIG. 3 and the receiving side shown in FIG. 5. The portion within the dotted line frame is related to the present invention.

FIG. 7a shows the control signal transmission situation, and FIGS. 7b and 7c show details of control signal transmission on the transmitting side and the receiving side. This corresponds to FIG.
Interface signals RS and SD from the processing device 10
are input to the transmitting side transmission device 18, and are time-division multiplexed and transmitted by the transmission section TR. At that time, the control signal
RS is transmitted as a command representing off to on and from on to off. In the receiving side transmission device 20, the transmitted signals RS and SD are sent to the receiving section REC.
Distributes to CD and RD (SD is output as RD, RS on/off is output as CD on/off).

Effects of the Invention As explained above, in the present invention, since a timer with buffer and delay time τ is provided in the transmission device serving as the relay transmission end, reliable data transmission can be performed without the need to receive the permission signal CS, and the line is It has advantages such as being able to absorb fluctuations in transmission delay of control signals when connected in tandem.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a data transmission system using tandem-connected communication lines, Fig. 2 is an explanatory diagram of the transmission procedure, and Figs. 3 and 4 are block diagrams showing details of each part in Fig. 1. FIG. 5 is a block diagram showing an embodiment of the present invention, FIG. 6 is a block diagram showing the configuration of a transmission device to which the present invention is applied, and FIG. 7 is an explanatory diagram of a control signal transmission situation. In the drawing, 18, 20, 22, 24 are transmission devices, 1
4 and 16 are communication lines, B is a buffer, and T is a timer.

Claims (1)

[Claims] 1. A communication line 14 having at both ends a transmission device 18 for time division multiplexing and a transmission device 20 for returning the time division multiplexed signals to individual line signals, a modem 22,
In a data transmission system in which communication lines 16 having 24 at both ends are connected in tandem, a buffer B for storing received data is provided in a transmission device 20 serving as one receiving end and the other transmitting end of the communication lines 14 and 16; A data transmission system comprising: a timer T which receives a carrier detection signal CD and generates a signal instructing the buffer to send data after a time difference τ between a transmission request signal RS and a permission signal CS.