JPS6112146A - Signal transmission system from terminal equipment - Google Patents

Abstract

PURPOSE:To prevent a reflection fault of a signal with simple constitution by providing a comparison means between a level of a reception signal and a level of a transmission signal in a terminal equipment and setting the transmission level of an incoming signal based on the output. CONSTITUTION:An outgoing signal toward terminal equipment T transmitted from a bus terminator ME is transmitted through an outgoing bus 13, subjected to attenuation corresponding to a bus line length up to the equipment T, received by a reception circuit 1 of the equipment T, transmitted to a CPU6, where the signal is analyzed. The level of the outgoing signal is detected by a reception level detector 2, converted into a DC voltage corresponding to the level and inputted to a comparator 4. On the other hand, a transmission circuit 3 is operated intermittently to transmit the incoming signal to the incoming bus line 14 and the DC voltage in response to the transmission level at transmission is inputted to the comparator 4. The comparator 4 compares two input voltages and output the result of comparison to a transmission level automatic adjusting device 5. The adjusting device 5 sets automatically the transmitted level of the incoming signal so that the level is coincident with the outgoing signal level.

Description

Detailed Description of the Invention (Technical Field of the Invention) The present invention relates to a method in which a bus terminal device and a plurality of terminal devices are connected by a time division multiplex digital bus, and information is exchanged between the two. In a division multiplexing digital signal transmission system, especially when the information sent from the bus terminal device to the terminal device (downlink signal) and the information sent from the terminal device toward the bus terminal device (uplink signal) are The present invention relates to a method for setting the output level of output signals in a terminal device of a system in which transmission is performed in the same direction on a division multiplex digital bus.

(Technical Background and Prior Art of the Present Invention) As shown in FIG. 3, the configuration of a time division multiplex digital bus in a system in which the present invention is implemented is as shown in FIG. The upstream bus line 14 and the upstream bus line 14 are separately packaged, and one of the bus lines, for example, the downstream bus line 13, is routed back and forth by the return bus line 12, so that the downstream signal and the upstream signal are routed separately. 11
The upper propagation direction is the same, so that the signal propagation delay time is the lower signal, and both the terminal equipment T
The bus line length is made to match the length of the bus line in the point call to which terminals 1 to Tn are connected, so that bits of signals from different terminal devices do not overlap.

By the way, the signals sent from the terminal devices Tl to Tn to the upstream bus line 14 are transmitted in the forward direction (
It propagates equally in both directions (direction towards the receiving end of the bus terminating device MEO) and in the opposite direction (direction towards the terminating resistor 15),
The forward direction signal is received by the bus termination device ME, and the reverse direction signal is absorbed by the termination resistor 15.

Generally, when the terminal devices T1 to Tn are connected to the bus 11, the electrical characteristics of the bus 11 at that connection point change to characteristics different from those of other parts. When the signal transmitted from the bus 11 propagates through the bus 11, it is reflected at the change point of the electrical characteristics (connection point of each terminal device T1 to Tn) with an intensity corresponding to the degree of the change, and the reflected wave is It propagates in the opposite direction to the signal propagation direction. For example, the terminal device Tn whose connection point to the upstream bus line N14 is closest to the receiving end of the bus terminal device MEiO (hereinafter, when a terminal device is referred to as far or near, it refers to the connection to the upstream bus line 14). Considering this, the signal sent from the terminal device tTn to the upstream bus 14 propagates in both forward and reverse directions at the connection point, and the signal in the forward direction is transmitted to the upstream bus 14 at the connection point.
4 after a time corresponding to the distance tn, the bus terminal device MP
The signal in the opposite direction reaches the O receiving end and is sent to the terminal equipment Tn-1 to T1.
For example, the component reflected at each connection point of the terminal device Tn-1 has a distance of "2C1n-+IJ"
Later, from the time when the forward signal reaches the receiving end of the bus termination device MEO, the signal travels back and forth over the distance u tn-,,tn, between the connection point of the signal sending terminal device i'rn and the reflection point. After some time, the bus terminator MEO receiver is reached. When the signal transmission level from the terminal device Tn is thick, the level of the reflected wave increases accordingly, and the reflected wave appears in the subsequent time slot of the regular signal (signal propagating in the forward direction) and A reflection failure is caused which destroys the data of the time slot.

To explain the above in detail with reference to the drawings, the level of the down signal at each point on the down bus line 13 is attenuated linearly as it approaches the bus termination device ME, as shown by the straight line 21 in FIG. increase. In addition, each terminal device T1 to T
Assuming that the output level of the upstream signal from n is constant,
As shown by a straight line 22 in FIG. 4, the level of the upstream signal at the receiving end of the upstream bus line 14 of the bus terminal ME increases linearly as the terminals T1 to Tn approach the receiving end of the bus terminal MEO. do. In such a state, the received waveform at the receiving end of the upstream bus line 14 is modeled and shown as shown in FIG. In FIG. 5, 31 represents the waveform (indicated by an envelope; the same applies to other signals) of the output signal from the terminal ftTn closest to the bus terminating device MEK at the receiving end of the bus terminating device MEO; 33 is the waveform of the reflected wave that is reflected at the branch point between the terminal device 'rn-t and the upstream bus line 14 and appears at the receiving end of the path termination device MEO. T
The waveform of the output signal of 1 at the bus termination device MEO receiving end is expressed as 3
4 shows the waveforms actually observed at the bus terminal device MFiO receiving end by combining the signals shown in 31 to 33 above. As shown in the signal waveform 33 above, the upstream signal sent from the terminal device located away from the bus termination device ME is greatly attenuated due to the transmission loss in the upstream bus line 14.

In addition, in the signal waveform 34 above, 341 and 344 are parts without reflection failure, and 342 and 343 are parts of the reflected wave 32.
The amplitude of each wave is increased by the amount of the reflected wave 32 in the area affected by the interference. In the above, 342
In the part 343, the ratio of the amplitude increase due to the reflected wave 32 to the reception level a of the upstream signal is small, so no actual damage will occur due to reflection failure, but in the part 343, the amplitude increase due to the reflected wave 32 to the reception level C of the upstream signal Since the rate of increase increases, reflection failure occurs and normal reception of upstream signals becomes impossible.

The reflection of the reverse direction signal as described above is reflected by each terminal device'rn,
- This occurs at all connection points of the TI, so at the receiving end of the upstream bus line 14, signals are received in multiple layers, as shown in the waveform photograph in Figure 7 (right side of the center). This makes it impossible to reproduce correct data from the signal. Generally, the degree of this reflection interference tends to increase as the length of the bus 11, the number of installed terminal devices T1 to Tn, the signal transmission speed, and the number of channels increase. A signal transmitted from a terminal device that is far from the bus termination device ME and has a large signal transmission loss on the bus is more susceptible to the above-mentioned reflection disturbance.

In order to eliminate the above-mentioned reflection disturbance, conventionally, a buffer amplifier is inserted between the bus 11 and the terminal devices T1 to Tn, and the output impedance of the terminal device 'rl-Tn as seen from the bus 11 side is increased. The configuration is such that reflection of reverse direction signals at the connection point of devices T1 to Tn to bus 11 is suppressed as much as possible, and the branching device used for this configuration is a two-system transmitting/receiving fusso amplifier. , it has a built-in stabilized power supply to operate it, making it large and expensive. Moreover, the branching device is required at the branching point for each of the cable terminals T1 to Tn, which makes it difficult to lay the cable and change the installation of the terminal device, which reduces system price and installation costs. This is a major obstacle to the reduction of

(Objective of the present invention) The present invention solves the above-mentioned conventional problems and provides a signal transmission method that can prevent signal reflection failure without using special circuit means such as a branching device including a buffer amplifier. With the goal.

(Summary of the present invention) Regarding reflection failure, when the reflection point is close to the signal reception point (reception end of the bus terminal device) and the time delay of the reflected wave is less than 1/10 of the received code, or the intensity of the reflected wave is When the level of the reflected wave is sufficiently lower than the intensity of the superimposed code, the reflection failure does not occur. The present invention particularly utilizes the latter of these characteristics.

In other words, from the bus terminal device to the terminal device, the sending signal (
In a system where the downlink signal (downlink signal) and the outgoing signal (uplink signal) from the terminal device to the bus termination device are transmitted in the same direction on the bus, the amount of attenuation that the downlink signal/signal receives during bus transmission is The total amount of attenuation received by uplink signals is approximately the same for all terminal devices.

Therefore, if each terminal device detects the received level of the downlink signal and sends out the uplink signal at a level that is a certain ratio to the received level, the uplink signal from each terminal device will be transmitted to the respective terminal device. The upstream signals from all terminal devices are attenuated in accordance with the length of the bus between the bus terminal device and the bus terminal device, so that the upstream signals from all terminal devices are at approximately the same level when received by the bus terminal device. In addition, with the above configuration, the upstream signal from the terminal device close to the bus termination device when connected to the upstream bus line is sent out at a low level, so the reflected wave of the upstream signal reaches the bus termination device. The current level can always be suppressed to a certain level or below, regardless of the branch point of any terminal device.

The present invention has obtained a new reflection interference removal method by utilizing the above-mentioned matters. Specifically, the level of the received signal (lower signal) and the level of the transmitted signal (upstream signal) are determined in the terminal device. A comparison means is provided, and the output level of the upper signal is automatically or artificially set based on the output of the comparison means.

(Embodiments of the present invention) FIGS. 1 and 2 are block diagrams showing first and second embodiments of the present invention, and T is a terminal device (T1 to T in FIG. 3).
Corresponds to n. ), 1 is a receiving circuit, 2 is a receiving level detector, 3 is a transmitting circuit, 4 is a comparator, 5 is an automatic transmission level adjuster, 6 is a central processing unit (so-called CPU), 7 is a display, and 8 is a The transmission level setters are respectively shown, and 9 and 10 are signal level measurement points of the down bus line 13 and the up bus line 14, respectively. The same symbols ``13'' and ``4'' as in Figure 3 are used for the bus lines, down bus lines, and up bus lines.'First, let us explain the operation of the first real ellipse shown in Figure 1. explain.

Bus termination device MI! ! The downlink signal for the terminal device T outputted from (FIG. 3) is transmitted by the downlink bus line 13,
The signal is attenuated by an amount corresponding to the bus length of the downlink bus line 13 to the terminal device T, is received by the receiving circuit 1 of the terminal device T, and is sent to the central processing unit 6 for analysis.

The downlink signal is also input to the reception level detector 2, and in response to this, the reception level detector 2 detects the reception level of the downlink signal at the terminal device T, converts it into a DC voltage, etc., and converts it into a comparator 4. Output to. On the other hand, the multiplication circuit 3 is connected to the upstream bus line 13.
It operates intermittently to send out an upstream signal to the comparator 4, and outputs a signal corresponding to the sending level at the time of the operation to the comparator 4.

The comparator 4 sends a signal based on the level comparison result of the two signals to the automatic output level adjuster 5, and the automatic output level adjuster 5 receives the output signal of the comparator 4 and inputs the signal to the comparator 4. The output level from the transmitting circuit 3 is automatically set so that the level of the signal corresponding to the output level of the upstream signal and the level of the downstream signal match. To explain the operating mechanism of the comparator 4 and the automatic transmission level adjuster 5 in more detail, the output signal of the comparator 4 controls the transmitter power supply voltage of the transmitter circuit 3, and lowers the power supply voltage to receive the signal. (The power supply voltage controlled in this way matches the output level of the above-mentioned signal.)
corresponds to ), or detect and hold the level of the uplink signal when it is actually sent out, input this held signal level to the comparator 4 and compare it with the level of the downlink signal, and output the signal from the comparator 4. A possible method is to set the transmitter power supply voltage of the transmitter circuit 3 using the comparison result output signal (the held signal level corresponds to the signal corresponding to the sending level of the stop signal).

When the central processing unit 6 sends an upstream signal to the upstream bus line 14 through the transmission circuit 3 in the above state, the signal level at the measurement point 9 on the downstream bus line 13 and the measurement point 10 on the upstream bus line 14 match, The objectives of the invention are achieved.

Next, the operation of the second embodiment of the present invention will be explained with reference to FIG.

The difference from the first embodiment is that the sending level of the upstream signal is not automatically adjusted, and the comparison results of the two signals from the comparator 4 are displayed on the display 7. The key point is that the output level of the upstream signal is manually set using the output level setter 8. When the output level setter 8 is adjusted until the display 7 shows that the received signal (downstream signal) level and the output signal (upstream signal) level match, the measurement points 9 of each upstream and downstream bus line are adjusted.
The signal levels at and 10 match and the object of the invention is achieved.

The present invention can be implemented in any bus system in which the downlink signal for the terminal and the two signals for the terminal device are transmitted in the same direction. Furthermore, the output signal level of each terminal device is not set so that the output signal level matches the input signal level, but the output signal level is set to maintain a constant relationship between both levels. l~ may be used to control.

The signal superimposition state of the upstream/downstream line 14 when the terminal device T configured as described above is connected to the bus 11 as shown in FIG. 3 will be explained with reference to FIG. In addition, Fig. 6 shows the above-mentioned 5th
Shown in a similar manner to the figure. That is, 41 represents the waveform (indicated by an envelope) at the receiving end of the /x terminal device MEO of the output signal of the terminal device Tn closest to the /x terminal device ME.

42 is the reflected wave that appears at the receiving end of the bus terminal device MEO after the output signal of the terminal device Tn is reflected at the branch point between the terminal device fttTn-i and the upstream line 14. 43 is the waveform at the bus termination device MEO receiving end of the output signal of the terminal device T1 which is farthest from the path termination device MFi, and 44 is the waveform at the bus termination device MEO receiving end where the signals shown in 41 to 43 above are combined and sent to the path termination device MFiO reception end. The waveforms actually observed at the edges are shown as models, and the 44 waveforms are 441, 441,
442, 443.444 are respectively 34 in the above figure 5.
This corresponds to 341, 342, 343, and 344 in the waveform.

In FIG. 3, the level of the downlink signal detected by the reception level detector 2 of the terminal device T1 farthest from the bus termination device MP is the level of the downlink signal detected by the reception level detector 2 of the terminal device Tn closest to the bus termination device ME. The level is higher than the level of the detected downlink signal by a level corresponding to the transmission loss in the line length II t1tn++ of the bus 11. The level of the upstream signal output from the transmitting circuit 3 is set based on the level of the downstream signal by the action of the comparator 4 and the automatic transmission level adjuster 5 or the transmission level setter 8 as shown in 17 above, so that the terminal Device T1
The level of the upstream signal sent from the above line length "t,
The level corresponding to the transmission loss at tnII is set higher than the level of the upstream signal sent from the terminal device Tn. That is, terminal devices far from the bus termination device ME output uplink signals at a high level corresponding to the line length of the bus 110 between them.

Therefore, as shown at 41.43 in FIG. 6, when the respective upstream signals output from the terminal device Tn and the terminal device T□ reach the receiving end of the bus terminal device MEO, they both have approximately the same level (that is, the waveform of 44). and a'Hb).

That is, as shown by the straight line ``23'' in FIG. 4, the incoming levels of the signals from each of the terminal devices T1 to Tn at the receiving end of the upstream bus line 14 of the bus termination device ME are all equal to t. .

Therefore, the influence of the reflected wave 42 on the upstream signal 43 from the terminal device T1 is extremely small compared to the case of the conventional example, as shown by the relationship between 443 and 444 in FIG. ), erroneous data detection does not occur at the bus termination device ME.

(Effects of the present invention) FIGS. 7 and 8 are waveform photographs showing the effects of the present invention, and are respectively a conventional example (one that does not have a level adjustment means in the transmitting circuit section of the terminal equipment fftT) and an example of the implementation of the present invention. This is an actual waveform observed with an oscilloscope at the receiving end of the bus terminating device ME in an example (the transmitting circuit section of the terminal device T has level adjustment means).

In Figures 7 and 8, the left side from the center is the bus termination device MF.
The waveform of the transmission signal from the terminal device 'rn closest to j is observed at the bus termination device MEO receiving end. The waveforms observed in each are shown.

As can be understood from FIGS. 7 and 8, conventionally, the signal waveform of the terminal device remote from the bus termination device ME is observed to have a waveform that overlaps many times due to signal reflection. However, in the case of the embodiment of the present invention, there is almost no influence due to signal reflection, so no overlap of waveforms is observed.

Furthermore, as is clear from the comparison between the right side and the left side from the center of Fig. 8, even if the distance between the terminal device T and the bus termination device MB is different, the transmission signal from the terminal device T is at almost the same level. Received by ME.

From the above, according to the present invention, the branch device installed at the branch point to the bus terminal device does not require a buffer amplifier and a power source to operate the buffer amplifier, and for example, the branch device can be installed with only a simple connector. The present invention is extremely effective in reducing system size, cost reduction, and operation cost.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams of embodiments of the present invention, Figure 3 is a block diagram of a time division multiplex digital signal transmission system implementing the present invention, and Figure 4' explains bus signal levels. Graphs, FIGS. 5 and 6 are diagrams illustrating received signal levels in the bus termination devices according to the conventional example and the embodiment of the present invention, respectively, and FIGS. 7 and 8 are graphs illustrating the conventional example and the implementation of the present invention, respectively. It is an oscilloscope photograph of the received signal waveform in the bus termination device ME according to an example. (Main symbols) MID...Bus terminal device t T (Tt~'rn)
...Terminal device 1...Receiving circuit 2...Reception level detector 3...Transmission circuit 4...Comparator 5...Sending level automatic adjuster 6...Central processing unit ft7...・Display 8...Output level setting i11...Bus 13...Down bus line
14...Inbound bus line. Figure 1 Figure 2 Figure 4 TIT2---------7yI ME -□4P request
Ifl Figure 5 Figure 6 Figure 7 Procedural amendment document Showa 2θ July//Date 1, Incident display Showa Care in hand Permission No. 7326. Relationship with the j3 incident
Applicant 4, Agent (f: 3308 Marunouchi Hetonzu Building, 2-6-2 Marunouchi, Chiyoda-ku, Tokyo) Contents of the amendments The following matters have been amended in the specification and drawings of the application as shown in the attached document. Note 1. On page 8, line 6, the word "futufa amplifier" is corrected to "buffer amplifier." 2. "Figure 3" in the drawing is corrected to the drawing submitted today. ,-) Agent Tani Teruo Yama: □ [hi]

Claims (1)

[Claims] 1. The transmission direction of the signal sent from the bus termination device and received by the terminal device and the transmission direction of the signal sent out from the terminal device and received by the bus termination device are on a time division multiplexed digital bus. In the terminal equipment of the time division multiplex digital signal transmission system, which is set to be the same at the terminal equipment, the received signal level and the transmitted signal level are compared for each terminal equipment, and the settings are made for each terminal equipment based on the result of this level comparison. A signal transmission method from a terminal device that transmits a signal to the time division multiplex digital bus according to a transmission level. 2. A signal transmission system from a terminal device according to claim 1, wherein the level comparison result is input to a signal transmission circuit to automatically set a transmission signal level. 3. The signal transmission method from the terminal device according to claim 1, wherein the level comparison result is displayed and the transmission signal level is artificially set based on this display.