JPH0245860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal transmission circuit, and particularly to a signal transmission circuit suitable for n:m communication in a loop-shaped communication path.

In a data communications network, multiple stations are connected in a multi-drop, loop, star, etc. network, but a loop is suitable from the standpoint of high speed response and high throughput. Furthermore, n:m communication, which enables communication with any station, is expected to be widely adopted in the future.

In order to realize n:m communication, unlike the case of 1:n communication, it is necessary to make sure that the data on the communication path goes around the communication path only once and does not exist on the communication path beyond one round. , this is one of the reasons why n:m communication is hindered from spreading because this is difficult.
It was hot.

FIG. 1 is a schematic diagram of loop communication. In FIG. 1, five stations A to E are connected to a loop-shaped communication path 51. In FIG. The direction of data transmitted through the communication channel 51 is fixed, for example, as A→B→C→D→E→A, as indicated by arrows in the figure. Furthermore, the transmitting end and receiving end of each station are connected to the communication path 51.

Each station A to E consists of a signal transmission circuit that performs serial-parallel conversion of transmitted and received data and frame control, a memory that stores data, an interface unit with the application side, and a command unit that controls these. be. It goes without saying that the command section may be constructed of either random logic or a microcomputer. Note that the signal transmission circuits of stations A to E are all composed of the same circuit.

In n:m communication, each station A to E operates in a repeat mode in which data received from an upstream station via the communication path 51 is sent as is to a downstream station, and in a transmission mode in which each station A to E itself transmits data to other stations. is required, and these two modes can be switched as needed.

Furthermore, each station A to E can transmit data to the communication path 51 only after receiving a transmission right signal indicating the transmission right.
This is also the time when it is confirmed that there is no frame following the transmission right signal. This transmission right signal is transmitted through the communication path 51.
There is only one above.

FIG. 2 shows an example of the structure of serial data to be transmitted. The serial data shown in Figure 2 is High Level
It follows the Data Link (hereinafter abbreviated as HDLC) procedure. The division of a frame, which is a collection of data, is indicated by a start flag 52 and an end flag 57. Both flags 52 and 57 have the same pit pattern, which is determined as "01111110". Start flag 52
followed by destination address 5 indicating the receiving station number.
3. A control unit 54, an information unit 55, and a destination address 53 that control the communication link status between two stations.
FCS (Frame Check Sequence) 5 performs an error check between the control section 54 and the information section 55.
6, and finally a termination flag 57.

There are various types of transmission right signals: “0” followed by “1”
When seven consecutive ``GA patterns'' (hereinafter referred to as GA patterns) are received, the seventh ``1'' is changed to ``0'' and this is used as a start flag, a combination of GA patterns following a frame of a certain pattern. There is a method to do this. In the former method using only GA patterns, if the idle data between frames is "1", it may change to "0" due to noise, so in general, the latter method using GA pattern following a frame with a specific pattern is
Use patterns.

The transmission right management station that generates and transmits the transmission right signal is fixed to one station in advance so that only one station exists at the same time on the communication path 51, or it is rotated sequentially, or This is determined by a method such as selecting one station from among all stations A to E each time.

Next, a conventional signal transmission circuit and the flow of transmitted frames will be explained using FIGS. 3 and 4.

Figure 3 is a block diagram of a conventional signal transmission circuit.
FIG. 4 is a frame flowchart for the case according to FIG. In FIG. 3, received data RD, which is a DC data string, received from a communication path 51 is transmitted through a serial-to-parallel conversion circuit 2 that converts serial data to parallel data, a GA detection circuit 3 that detects a GA pattern of a transmission right signal, and a GA detection circuit 3 that detects a GA pattern of a transmission right signal. A detection circuit 4 that detects the flag 52 or termination flag 57, and a first selection circuit 1 that selects data to be transmitted to the communication channel 51 in repeat mode.
4 is input.

The data converted into parallel data by the serial/parallel conversion circuit 2 is temporarily stored in the reception buffer register 5, and then transferred to a memory (not shown) via the parallel data bus 20. On the other hand, in GA detection circuit 3
The detection of the GA pattern is stored in the status register 6, and the status register 6 receives the transmission start permission signal 22.
is output to the transmission control circuit 9. The flag detection circuit 4 also detects a start flag 52 or an end flag 5.
7 is received and stored in the status register 6. This indicates that frame transmission has started or ended. The contents of the status register 6 are reported to a command unit (not shown) via the parallel data bus 20 as necessary.

Information for controlling the transmission and reception of data from the command section is stored in the control register 7. Further, data to be transmitted to the communication path 51 is stored in the transmission buffer register 8 from the memory at any time. The transmission data stored in the transmission buffer register 8 is converted from parallel data to serial data by a parallel-to-serial conversion circuit 10, and an FCS 56 is generated by an FCS generation circuit 11. In addition, the GA pattern is the GA generation circuit 12,
The start flag 52 and the end flag 57 are generated by the flag generation circuit 13.

The transmission data TD sent to the communication path 51 in the repeat mode or the transmission mode is sent to the first selection circuit 41 as the reception data RD or the serial/parallel conversion circuit 10, the FCS generation circuit 11, and the flag generation circuit 12.
And one of the outputs of the second selection circuit 15 which selects one of the outputs from the GA generation circuit 13 is selected. Note that a transmission/repeat switching signal 26 and a transmission switching signal 27 for selecting the first selection circuit 14 and the second selection circuit 15, respectively, are generated by the transmission control circuit 9.

Transmission/repeat switching signal 26, transmission switching signal 2
7. Signals that control the parallel/serial conversion circuit 10, FCS generation circuit 11, flag generation circuit 12, and GA generation circuit 13 are generated by the transmission control circuit 9, and the transmission control circuit 9 receives the transmission request signal 2 in the control register 7.
3. It operates according to the repeat signal 24 and the transmission start permission signal 22 from the status register 6.

Reception data RD and transmission data TD are transmitted and received in synchronization with clock CLK from a separately provided clock generation circuit. Since the clock for reception and the clock for transmission have a repeat mode in loop communication, they need to be in the same phase, and can be a common clock CLK.

Next, the flow of frames will be explained with reference to FIG. Now, assume that the transmission right management station is station A, and the station requesting transmission data is station C. Furthermore, it is assumed that "1" is transmitted between frames in which no data is transmitted.

Station A switches from repeat mode to transmission mode at time _t1 , transmits the transmission right frame TN and GA pattern, and thereafter transmits idle data "1".
Send. Stations B to E are in repeat mode, but when station C receives the transmission right signal, it switches to transmission mode and prepares to transmit frame FC.

The data to be transmitted has a total time delay of the time delay caused by the communication path 51 and the time delay caused by the repeat mode and driver-receiver circuit of each station, but the phase shift due to the time delay for one round is corrected by a certain station, All stations A to E can transmit and receive correctly.

Station B sends the received data to station C in repeat mode.
Send to. Since station C has a transmission request, it is waiting to receive a transmission right frame TN. Then, upon receiving the start flag 52 of the transmission right frame TN,
The fact that the flag detection circuit 4 has detected the start flag 52 is stored in the status register 6 and reported to the command section. The command unit takes in and decodes the data received from the reception buffer register 5 via the parallel data bus 20, and the received frame becomes a transmission right frame.
If it is determined that the pattern is the same as TN, the command unit switches to the transmission mode and transmits the frame FC when the GA detection circuit 3 detects the GA pattern, so the command unit activates the repeat signal 24 of the control register 7.
to reset state. As a result, station C has GA
When the detection circuit 3 detects the GA pattern, it outputs the transmission start permission signal 22, and at time _t2 , the transmission/repeat switching signal 26 changes the selection signal of the first selection circuit 14 from the received data RD to the second selection circuit that becomes the transmission data. Switch to output 15.

Since stations D and E are in the repeat mode, the received data RD from the communication path 51 of the upstream station is sent as is to the communication path 51 of the downstream station. The station that matches the contents of the destination address 53 in the frame FC transmitted by station C transfers the frame FC to the command unit.

After being transmitted from station A, the transmission right frame TN goes around the communication path 51 and returns to station A again. The transmitted right frame TN is no longer needed in n:m communication, so it is deleted by the station A that transmitted it. The first method for erasing is to confirm the completion of transmission of the transmission right frame TN and GA pattern, which are generated by the transmission control circuit 9 and reported to the command unit via the transmission completion signal 21, the status register 6, and the parallel data bus 20. and the transmitted right-to-send frame.
The TN goes around the communication path 51 and returns to station A, and the start flag 52 of the transmission right frame TN is detected by the flag detection circuit 4.
status register 6, parallel data bus 2
Using the start flag detection signal reported to the command section via t3, the command section requests the repeat signal 24 of the control register 7 to enter the repeat mode, and at time _t3 , the command section requests the repeat signal 24 of the control register 7 to enter the repeat mode. There is a method of switching the station A to the repeat mode by using the transmission/repeat switching signal 26.

The second method is to
There is a method in which the command unit requests the repeat signal 24 to enter the repeat mode after the command unit is notified that the TN termination flag 57 has been received, and the station A is placed in the repeat mode.

Here, according to the first method, after the completion of transmission and detection of the start flag are reported to the command section, the command section makes a determination, instructs switching to repeat mode, and the first selection circuit 14 selects the received data RD. Transmission data
Since it takes time to output to TD, it enters repeat mode while receiving the transmission right frame TN.
The second half TR of the transmission right frame TN remains and is transmitted to the downstream station. On the other hand, according to the second method, if the transmission data continues after the transmission right frame TN, the beginning of the transmission data will be erased due to the processing delay from frame detection at the command unit to the repeat mode instruction. It will be done.

FIG. 4 shows the case of the first method, in which the transmission mode M _T is from time t ₁ to time t ₃ and the repeat mode M _R is from time t ₃ onward.

Similarly, station C receives the transmission frame sent by itself.
When the FC goes around communication path 51 and returns to its own station,
Erase the transmitted frame FC. This erasure method includes the first and second methods, similar to the erasure of the transmission right frame TN at station A described above. Figure 4 shows the first
In this case, the second half TR of the transmission frame FC is sent out to the communication path 51 in the same way as the second half TR of the transmission right frame TN remains. In station C, the transmission mode M _T is from time t ₂ to time t ₄ , and the repeat mode M _R is from time T ₄ .

As described above, in both the first and second methods, it is not clear how to distinguish between frames that should be erased and frames that should be repeated and sent to a downstream station, and there are drawbacks as described below. In other words, the remaining transmission right frame TR, which is unnecessary data, and the remaining transmission frame FR
Due to the infinite circulation on the communication path 51, the flag detection circuit 4 of each station A to E operates, increasing the processing in the command section and preventing damage to the original processing operation of the command section. Moreover, the load factor of the communication path 51 increases. The load factor on the command unit due to the circulation of unnecessary data is such that processing with one frame remaining for each loop continues indefinitely.

As is clear from the above description, according to the prior art, the load factor of the command unit is high, and the communication path 51
The disadvantage is that the load factor is high, making it impossible to transmit correct frames.

The present invention has been made in view of the above, and its purpose is to transmit signals that can reduce the load factor of the command unit and the communication path, and that can correctly circulate the transmitted data through the communication path. The purpose is to provide circuits.

In the present invention, a plurality of stations transmit data received from an upstream station via n:m communication via a loop-shaped communication path, and a station requesting transmission of transmission data from its own station sends a transmission right signal indicating a transmission right. When received from the upstream station,
In a signal transmission circuit that transmits data by switching from a repeat mode in which data received from the upstream station is transmitted to a downstream station to a transmission mode in which the transmission data is transmitted to the downstream station, the transmission right signal is a transmission right frame. A switching register that sets either the transmission mode or the repeat mode in combination with the following GA pattern, and a transmission that transmits either the data received from the upstream station or the own station depending on the state of the switching register. a selection circuit that selects whether it is data; a frame detection circuit that detects that one frame of data has been received;
a first AND circuit that receives as input a transmission completion signal indicating completion of transmission from its own station and a frame detection signal that is an output of the frame detection circuit; and a repeater that requests the repeat mode and the output of the first AND circuit. a second AND circuit that receives as inputs a transmission request signal requesting transmission from its own station and a transmission start permission signal based on a transmission right signal indicating a transmission right received from the upstream station; The switching register is set to the first state by the output of the first AND circuit to select the repeat mode, and is maintained in the second state by the output of the second AND circuit to select the repeat mode. When the transmission mode is selected and the local station starts transmitting data, the switching register is switched to the second state, and after the local station has completed transmission, the switching register is switched to the second state when the data that has gone around the communication path is received. The present invention is characterized in that it includes a transmission control circuit in which the register is switched to the first state and the data completes by making only one round through the communication path.

The embodiment of the present invention shown in FIG. 5 and the sixth embodiment will be described below.
This will be explained in detail using FIG.

FIG. 5 is a block diagram showing an embodiment of the signal transmission circuit of the present invention. The same parts as in FIG. 3 are designated by the same reference numerals, and the explanation thereof will be omitted here. In FIG. 5, the transmission control circuit 9' is a frame detection circuit 30,
It is composed of a first AND circuit 31, an OR circuit 32, a switching register 33, a second AND circuit 34, and a transmission end generation circuit 35, and generates a transmission end generation circuit that indicates that the own station is in transmission mode and has completed transmitting a frame. The frame detection circuit 30 which receives the transmission completion signal 21 generated by the circuit 35 and the outputs of the flag detection circuit 4 and reception buffer register 5 as inputs receives one frame and detects that the termination flag 57 has been received. AND circuit 31 which receives as input the frame detection signal 36 from the frame detection circuit 30 shown in FIG.
output and repeat signal 2 from control register 7
The switching register 33 is set to a reset state by the output of the OR circuit 32 which receives 4 and 4 as input, and the switching register 33 generates the transmission/repeat switching signal 26 for the first selection circuit 14.

FIG. 6 shows the flow of frames in FIG. 5 when station A (see FIG. 1) is a transmission right management station and station C is a data frame transmitting station. Station A switches from repeat mode M _R to transmission mode M _T at time _t1 , transmits the transmission right frame TN and the GA pattern, is set to the transmission completion state, and receives the termination flag 57 of the transmission right frame TN which has completed one cycle. When the process is finished, the switching register 33 is reset at time _t7 , and the repeat mode M _R is switched again. As a result, the frame following the completed transmission right frame TN can be transmitted from the upstream station to the downstream station, and the remainder of the completed transmission right frame TN is not transmitted on the communication path 51 (see Figure 1). .

Here, the time _t7 at which station A switches to the repeat mode M _R is after the end of station A's GA pattern transmission, and the completion of transmission is set at the end of GA pattern transmission. Therefore, the time _t7 at which the mode is switched is when station A finishes transmitting the GA pattern or when the termination flag 57 (see FIG. 2) of the completed transmission right frame TN is received, whichever is later.

Station C receives the transmission right frame TN and the GA pattern, is switched from repeat mode M _R to transmission mode M _T at time _t2 , and transmits frame FC. After the frame FC has gone around the communication channel 51, when station C receives the end flag 57 of the frame FC,
At that time t ₇ , from transmission mode M _T to repeat mode
Can be switched to _MR .

The state of the transmission/repeat switching signal 26 which is the output of the switching register 33 in this case is shown in FIG. 7 for each station A to E.

According to the embodiment of the present invention described above, as is clear from the above description, the processing of the command section is reduced, and the load factor of the command section can be reduced by about 10%.

The frames used in the explanation of the above embodiments are as follows:
Although the configuration shown in FIG. 2 was used, the effect will not change even if frames with other configurations are used. In this case, if the patterns of the start flag 52 and the end flag 57 are different, the GA pattern will also be different.
Needless to say, it is necessary to change the GA generation circuit 13, GA detection circuit 3, flag generation circuit 12, and flag detection circuit 4 to correspond to the adopted pattern.

Further, a delay circuit that delays the transmission time of the GA pattern may be provided in the receiving section of the transmission right management station. In this case, since the time when the transmission right frame TN goes around the communication path 51 and returns to the transmission right management station is after the GA pattern is transmitted, the _repeat M The effect will not change.

As explained above, according to the present invention, since it is possible to prevent unnecessary data from being generated, it is possible to reduce the load factor of the command unit and the communication path, and also to prevent transmission data from disappearing and correct transmission data. This has the effect of making it possible to transmit the information to each station through one round of communication channels.

[Brief explanation of the drawing]

Fig. 1 is a schematic block diagram of loop communication, Fig. 2 is a block diagram of a conventional transmission signal circuit, Fig. 3 is a block diagram of a conventional signal transmission circuit, and Fig. 4 is a frame diagram according to Fig. 3. Flowchart, FIG. 5 is a block diagram showing one embodiment of the transmission signal circuit of the present invention, FIG.
The figure is a flowchart of a frame corresponding to FIG. 4 in the case of FIG. 5, and FIG. 7 is a diagram showing the state of the transmission/repeat switching signal, which is the output of the switching register of FIG. 5, for each station. 9'...Transmission control circuit, 14...Selection circuit, 2
1... Transmission completion signal, 22... Transmission start permission signal, 23... Transmission request signal, 24... Repeat signal, 26... Transmission/repeat signal, 30... Frame detection circuit, 31... First AND circuit, 32
... OR circuit, 33 ... switching register, 34 ...
Second AND circuit, 35... Transmission end generation circuit,
36...Frame detection signal, 51...Communication path, A
~E... Bureau.

Claims (1)

[Claims] 1 Multiple stations transmit data received from an upstream station via n:m communication via a loop-shaped communication path, and a station that requests transmission of data from its own station sends a transmission right signal indicating a transmission right from the upstream station. When received, the transmission right signal is transmitted in a signal transmission circuit that transmits data by switching from a repeat mode in which data received from the upstream station is transmitted to a downstream station to a transmission mode in which the transmission data is transmitted to the downstream station. a switching register that sets either the transmission mode or the repeat mode, and the data received from the upstream station or the own station depending on the state of the switching register. A selection circuit that selects transmission data to be transmitted, a frame detection circuit that detects that one frame of data has been received, a transmission completion signal that indicates the completion of transmission of the own station, and a frame detection signal that is the output of the frame detection circuit. a first AND circuit that receives as inputs the output of the first AND circuit and the repeat signal that requests the repeat mode; a transmission request signal that requests transmission from its own station; a second AND circuit that receives as input a transmission start permission signal based on a transmission right signal indicating a transmission right received from an upstream station, and the switching register enters the first state at the output of the first AND circuit. The repeat mode is selected by the output of the second AND circuit, and the transmission mode is selected by being held in the second state by the output of the second AND circuit, and when the local station starts transmitting data, the switching register is Second
When receiving the data that has gone around the communication channel after completion of transmission, the switching register is switched to the first state, and the transmission ends when the data goes around the communication channel only once. A signal transmission circuit comprising a control circuit.