JPH0666735B2 - Optical fiber communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber communication system for bidirectional communication using one optical fiber.

<Summary of the Invention> The present invention enables bidirectional optical fiber communication even when power is turned on or reset at any timing by transmitting in the transmission mode for a time longer than the maximum transmission time when the power is turned on or reset. I am trying to establish it.

<Background of the Invention> The applicant of the present invention has recently proposed an optical transmitter / receiver capable of bidirectional communication with a single optical fiber (Japanese Patent Application No. 58-198063). In this type of device, it is necessary to switch between transmission and reception. In this case, for example, if the partner station is in the transmission mode, it is necessary to switch the transmission / reception with good timing so that the local station is in the reception mode. is there.

Therefore, in order to perform this switching correctly, a method has been proposed in which one optical transmitter / receiver is the master unit and the other optical transmitter / receiver is the slave unit, and the transmitter / receiver modes of the master unit and the slave unit are switched based on the instruction of the master unit ( Electronic Chemistry, May 1980 issue,
55-59).

However, in order to implement this method, it is necessary to manufacture two models, a master unit and a slave unit, as optical transceivers, which not only increases the mass production cost but also makes the handling and management complicated, especially at the time of installation. Had the problem that it was necessary to pay attention to the combination of the master unit and the slave unit.

Therefore, the inventor has recently developed a new optical fiber communication system that enables bidirectional optical fiber communication with one type of optical transmitter / receiver without distinguishing between the master unit and the slave unit. This communication system, when detecting the end of transmission during the transmission mode, switches to the reception mode and waits for reception from the partner station, and when no signal continues for a predetermined time during the reception mode, The partner station determines that it has completed the transmission and switched to the reception mode, switches to the transmission mode and transmits data. Therefore, according to this communication system, smooth bidirectional communication can be realized without collision of signals from both sides during normal operation.

However, as a result of further examination of this communication system, at power-on or reset, depending on the timing, when the own station also starts transmission at the same timing as the partner station starts transmission, the following will be the same timing. It was found that the mode switching between transmission and reception is performed, which makes it difficult to communicate between the two stations.

<Object of the Invention> The present invention is for solving the above problems,
An object of the present invention is to provide an optical fiber communication system capable of establishing optical fiber communication at any timing when power is turned on.

<Structure and Effect of the Invention> In order to achieve the above object, the present invention is a communication system for performing bidirectional communication between optical transmission / reception devices connected by a single optical fiber, wherein each of the optical transmission / reception devices comprises: A means for switching from the transmission mode to the reception mode when the end of transmission is detected in the transmission mode, a means for switching from the reception mode to the transmission mode when the no-signal state continues for a predetermined time in the reception mode, and power-on. Alternatively, at the time of resetting, a means for switching from the transmission mode to the reception mode after transmitting in the transmission mode for a time longer than the maximum transmission time is provided.

According to the present invention, since bidirectional communication can be performed with one type of optical transmitter / receiver without providing a distinction between the master unit and the slave unit, it is sufficient to manufacture one type of optical transmitter / receiver, and the mass production cost is low. Not only is it easy to handle and manage, but there is no need to pay attention to the combination of the master unit and the slave unit during installation.

In addition, when the power is turned on or reset, it is configured to transmit for a time longer than the transmission time of the partner station, so bidirectional communication can be established regardless of the timing of turning on the power, etc. This system can be adopted, and the remarkable effects of achieving the object of the invention are achieved.

<Description of Embodiments> FIG. 1 shows an example of the configuration of an optical transmitter / receiver used in the optical fiber communication system of the present invention.

The apparatus shown in the figure comprises an optical transmission module 2 for executing data transmission / reception with respect to one optical fiber 1, and a control circuit unit 3 for controlling the transmission / reception operation of the optical transmission module 2.

The optical transmission module 2 has a transmission / reception mode switching signal T / R.
Is provided, and when the level of this T / R input is "LOW", it is set to the transmission mode, and when it is "High", it is set to the reception mode. In this transmission mode, when data is input (indicated by IN in the figure) from the transmission LS 14 (described later) of the control circuit unit 3, this data is converted into an optical signal and output. Further, when the optical signal from the partner station is received in the reception mode, the optical signal is converted into an electric signal and output to the transmission LSI 4 (indicated by OUT in the drawing). The input IN and the output OUT of the optical transmission module 2 are active at "LOW", and emit light when the input IN is "LOW" and extinguish when the input IN is "High" during the transmission mode. Further, in the reception mode, the output OUT becomes “LOW” when light enters the optical transmission module 2, and becomes “High” when no light enters. During transmission mode, output OUT is "Hi
"gh".

The control circuit unit 3 includes a delay time setting unit 5, a transmission LSI 4, a reception end detection circuit 6, a transmission end detection circuit 7, etc. as its main components.

The delay time setting unit 5 includes resistors R ₁ and R ₂ , a capacitor C, a transistor Q ₁ and a Schmitt trigger inverter 8. When the power supply Vcc is turned on, the output A of the transistor Q ₁ becomes the resistor R ₁ It falls from "High" to "LOW" with a delay of time t ₁ determined by the value of the capacitor C. Therefore, the output B of the Schmitt trigger inverter 8, after power Vcc, the process proceeds to "High" from a time t ₁ later "LOW".

The LSI 4 for transmission (for example, product name "IM1602") is an input pin
The 8-bit parallel signals input from TBR _{1 to} TBR ₈ are converted into serial signals, which are output from the output pin TRO to the optical transmission module 2, and also input from the optical transmission module 2.
The serial signal input via RRI is converted into parallel signals and output from output pins RBR _{1 to} RBR ₈ .

The reception end detection circuit 6 is for detecting the end of the reception operation in the own station, and when the optical transmission module 2 is in the reception mode (T / R input is “High”), the delay circuit 9
The counting is started with a delay of the time t ₂ set in step 1 and the time t during which the output OUT of the optical transmission module 2 is in the "High" state is measured. This time measurement is performed by the clock generation circuit 10
Is performed by counting the clock CL from the optical transmission module 2 and the output value of the optical transmission module 2 becomes “LOW”, the counted value is reset. Then, when the time t reaches the time t ₃ corresponding to one frame of the serial signal, it is determined that the partner station has switched from the transmission mode to the reception mode, and the own station is switched from the reception mode to the transmission mode. The pulse C for switching is output.

The transmission end detection circuit 7 is for detecting when the optical transmission module 2 has finished transmitting data to the partner station, and the optical transmission module 2 is in the transmission mode (T / R input is “LOW”). ), The transmission LSI4 sends TRE before the frame starts.
The end of transmission is detected using the signal output from the pin, and pulse D is output. This output is normally "LOW" and becomes "High" in response to the pulse D.

Each output side of the transmission end detection circuit 7 and the reception end detection circuit 6 is connected to a flip-flop 12 via an OR circuit 11. The flip-flop 12 receives the signal E from the OR circuit 11 every time the end of transmission or the end of reception is detected, and the rising of the signal E causes the output F of the flip-flop 12 to invert the previous state. The output F of the flip-flop 12 and the output B of the Schmitt trigger inverter 8 are input to the AND circuit 13, and this AND output is given to the optical transmission module 2 as a T / R input.

FIG. 2 shows T when the power of the partner station is off.
/ R shows the temporal movement of the input, and under this state, the output B of the Schmitt trigger inverter 8 and the output OUT of the optical transmission module 2 remain "High".

When the T / R input is currently in the "LOW" (transmission mode) state, the transmission end detection circuit 7 detects the end of transmission and outputs the pulse D
When the pulse D rises, the output signal E of the OR circuit 11 rises, and by catching the rise of the signal E, the flip-flop 12 inverts from "LOW" to "High". Therefore, the AND circuit 13 has the output B of the Schmitt trigger inverter 8 in the "High" state and the "Hig
The output F of the flip-flop 12 in the "h" state is input, whereby the output of the AND circuit 13, that is, the T / R input of the optical transmission module 2 becomes "High", and the transmission mode is switched to the reception mode. become.

The T / R input becomes “High”, and the predetermined delay time t ₂
After the elapse, the reception end detection circuit 6 starts measuring the time t during which the output OUT of the optical transmission module 2 is in the "High" state. In this case, the output OUT continues to be "High", so the time corresponding to one frame of the serial signal
When only t _{3 has} elapsed, the reception end detection circuit 6 outputs the pulse C
(Pulse width t ₅ ) is output. The output signal E of the OR circuit 11 rises at the rise of this pulse C, and the output F of the flip-flop 12 is also inverted to "LOW", whereby the T / R input of the optical transmission module 2 becomes "LOW". , The reception mode is switched to the transmission mode.

The timing of switching to the transmission mode and the timing of frame start do not always match, and after switching to the transmission mode, one frame starts to be transmitted after a certain time t _{4 has} elapsed, and one frame after the time t _{3 has} elapsed. The transmission ends. The end of transmission of this frame is detected by the end-of-transmission detection circuit 7, and mode switching from transmission to reception is executed based on the output pulse D of the end-of-transmission detection circuit 7. In the same manner, the transmission / reception operation and the mode switching are repeatedly executed, but in this case, the maximum value of the time t ₄ is the time t _4.
Since it corresponds to ₃ (one frame of the serial signal), the maximum value of the transmission time t ₆ is 2t ₃ .

Therefore, in the present invention, when the power is turned on or reset, the delay time t ₁ of the output B of the Schmitt trigger inverter 8 is set to the maximum transmission time in order to establish the communication state even if the transmission timing matches with the transmission timing of the partner station. It is set larger than 2t ₃ . This time t ₁ can be adjusted by changing the circuit constant of the delay time setting unit 5, for example, the resistance R ₁
If the value of or capacitor is increased, the time t ₁ becomes longer.

FIG. 3 shows T / T when the power of the other station is turned on at the same time when the own station is switched from the reception mode to the transmission mode.
The time movement of the R input is shown.

In FIG. 3, when the T / R input of the own station becomes "LOW" and the power supply Vcc of the other station is turned on at the same time, the output B of the Schmitt trigger inverter 8 in the other station is in the "LOW" state. After the time t ₁ continues, the signal becomes “High”, and the transmission end detection circuit 7 detects the end of transmission, and the T / R
The input is in the "High" state.

On the other hand, the local station waits for the time t ₇ (corresponding to the time (t ₃ + t ₄ ) in FIG. 2) required for transmission and then T
The / R input switches to the "High" state, and the reception mode is entered.
In this case, since the time t ₁ is set longer than the maximum transmission time 2t ₃ , the relationship of t ₁ > t ₇ is established, and the own station can receive the optical signal from the other station. Therefore, the data during the time t ₇ collides with each other and is wasted, but thereafter, communication is established and smooth bidirectional communication is performed.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an example of an optical transmitter / receiver used in the communication system of the present invention, and FIGS. 2 and 3 are time charts of the example of the device shown in FIG.

Claims (1)

[Claims] 1. A communication system for performing bidirectional communication between optical transmission / reception devices connected by a single optical fiber, wherein each optical transmission / reception device detects the end of transmission during a transmission mode. Means for switching from the transmission mode to the reception mode, and when the no-signal state continues for a predetermined time during the reception mode,
An optical fiber communication system comprising: means for switching from a reception mode to a transmission mode; and means for switching from a transmission mode to a reception mode after transmitting in the transmission mode for a time longer than the maximum transmission time when the power is turned on or reset.