JPS647528B2 - - Google Patents

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a transmission system using a loop-shaped transmission path. The present invention relates to a communication control device in which a primary station receives a message from a station.

(Background Art) FIG. 1 shows a conventional transmission system using a loop-shaped transmission path. In Fig. 1, this transmission system connects a primary station P and a plurality of secondary stations a, b, c, and d in sequence, and here uses a so-called high-level data link control line (referred to as an HDLC line). It is assumed that the Figure 2 (a) and (b) respectively show the message frame I _o (n indicates one of the secondary station addresses a, b, c, and d) transmitted on this HDLC line.
An example of polling frame UP is shown. In Figure 2, F is a synchronization pattern, A is an address part, C is a control part, I is a message part,
FCS is a frame check sequence, B is a global address, and UP is a polling command.
Figure 3 shows that in the transmission system shown in Figure 1, 1
Next station P sends message frames I _a addressed to secondary stations a, c, and d,
Following I _c and I _d , group polling UP ₁ is sent all at once to the HDLC line, and on the other hand, secondary stations _{a and c that have transmission requests send messages I a1 ,}
This is a time chart showing how the primary station P transmits I _c1 and receives it. As shown in FIG. 3, the primary station P receives the message frames I _a ,
I _b , I _c , polling frame UP ₁ and secondary station a,
The message frames I _a1 and I _c1 transmitted from c are sequentially received. The primary station P must use some means to distinguish between the messages I _a , I _b , I _c transmitted by itself and the messages I _a1 , I _c1 transmitted from the secondary station. Conventionally, various methods for this purpose have been considered.

FIG. 4 shows a communication control device CCE including a processing section CTL connected to a central processing unit CPU and a line connection section LCT connected to a loop transmission path LOOP. In FIG. 4, the line connection unit LCT is composed of a transmitting unit 1 and a receiving unit 2, which exchange signals with the transmission path LOOP, and a reception determining unit 3. The receiving unit 2 receives the message transmitted from the transmitting unit 1, the polling frame, and the message transmitted from the secondary station. The reception determination unit 3 determines whether the received message is a message transmitted from the local station, and does not send the message transmitted from the local station or the polling frame to the processing unit CTL, but sends the message transmitted from the secondary station to the processing unit CTL. Only the processing part
Send to CTL. However, in general, the communication control device CCE of the primary station is provided with the same number of reception determination sections 3 as the reception sections 2, and as the number of lines increases, the space occupied in the device increases, assembly, and adjustment. An increase in man-hours and, in turn, an increase in price is unavoidable.

FIG. 5 shows another communication control device CCE, in which the receiving section 2 receives all telegram frames transmitted from the transmitting section 1, polling frames, and telegram frames transmitted from the secondary station, and sends them to the processing section CTL. According to the software of the processing unit CTL, it is determined whether the message was sent from the local station or not, and only the message from the secondary station is processed as valid. However, the transmission line
Since LOOP is in a loop, the primary station P will receive the message addressed to the secondary station even while it is transmitting, and therefore the communication control device
The CCE must control transmission and reception at the same time, and for the communication control device CCE, this results in full-duplex communication, which imposes an unnecessary load and causes a decrease in total throughput.

(Object of the invention) The object of the invention is to eliminate these drawbacks,
A delay circuit section is connected in a dependent manner between the transmission section of the line connection section and the transmission line loop, and the delay circuit section delays the message frame and polling frame transmitted from the transmission section by a certain period of time to the transmission line LOOP. and the receiving unit of the line connection unit starts receiving after the transmitting unit completes transmission of the polling frame, and processes messages received after the polling frame as being from the secondary station, The goal is to achieve half-duplex communication.

(Structure and operation of the invention) FIG. 6 is a block diagram showing an embodiment of the invention. The delay circuit section 4 is subordinately connected to the transmission section 1 of the line connection section LCT, and a transmission path LOOP is connected to the end thereof. FIG. 7 shows details of the delay circuit section 4. Reference numeral 5 denotes a transmitting circuit, which is a part of the transmitting section 1 shown in FIG. 6, and is composed of, for example, a commercially available LSI.
6 is a shift register write circuit, 7 is a shift register, and 8 is a shift register read circuit.

Next, the operation will be explained.

In FIG. 3, if the primary station P starts receiving the polling frame UP ₁ immediately after completing transmission, it will not be able to receive part of the polling frame UP ₁ that it sent, and will be unable to receive it during the unreceivable period. T ₀ occurs. Therefore, as shown in FIG.
The signal from the transmitter 1 is delayed by a certain amount of time and transmitted to the transmission path LOOP, while the receiver 2 immediately starts receiving the polling frame UP ₁ after the transmitter 1 completes transmitting it to the delay circuit 4. and
To be able to receive polling frame UP ₁ without losing it.

Here, as an embodiment based on the present invention, a case will be described in which the delay circuit section 4 provides a delay time of a length corresponding to the time during which the polling frame UP ₁ is transmitted. In FIG. 6, message frames I _a , I _c , I _d and polling frame UP ₁ are sent from the transmitter 1.
is sent to the delay circuit section 4, the delay circuit section 4 is designed to provide a delay time corresponding to the time during which the polling frame UP ₁ is transmitted. The message frame I _a and the like transmitted from to the transmission path LOOP are output with a corresponding delay. That is, in FIG. 8, at time t _R when the primary station starts receiving, the polling frame UP ₁ is still in the delay circuit section 4 (point B), and the polling frame UP ₁ transmitted by the own station is
can be completely received (point C). Therefore,
The messages after the polling frame UP ₁ are passed to the processing unit CTL as being message frames I _a1 and I _c1 from the secondary station with a transmission request. On the other hand, since the transmission is completed at the time t _R , no load is placed on the processing unit CTL. Half-duplex communication is thus achieved.

The function of delaying information from the transmitter 1 is performed by a shift register 7 shown in FIG. Since the polling frame _UP1 normally consists of 48 bits, in the case of the above embodiment, it is only necessary to shift by 48 bits using the shift register 7. That is, it is possible to obtain a delay time corresponding to the time for transmitting 48 bits of polling frame _UP1 .

(Effects of the Invention) As explained above, in the present invention, by connecting the delay circuit section to the transmitting section, half-duplex communication is achieved in order to reduce the load on the primary station without reducing transmission efficiency. , the total throughput of the communication control device can be effectively utilized.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the state in which the primary station and secondary station are connected by a loop-shaped transmission line, and Figure 2 is
A pattern diagram showing an example of a message frame and a polling frame in an HDLC line, Fig. 3 is a time chart showing transmission and reception, Figs. 4 and 5 are block diagrams showing a conventional communication control device, and Fig. 6 is a main A block diagram of a communication control device showing one embodiment of the invention,
FIG. 7 is a detailed block diagram of the delay circuit section 4, and FIG.
The figure is a time chart showing transmission and reception according to an embodiment of the present invention. P...Primary station, a, b, c, d...Secondary station, A
...loop-shaped transmission line, LCT ... line connection section,
CCE...Communication control device, CTL...Processing unit, 1...
...Transmission section, 2...Reception section, 3...Reception determination section, 4
... Delay circuit section, 5 ... Transmission circuit, 6 ... Shift register write circuit, 7 ... Shift register, 8
...Shift register read circuit.

Claims (1)

[Claims] 1. A primary station and a plurality of secondary stations are connected through a loop-shaped transmission path, and group polling is performed from the primary station to the secondary stations. In the communication control device of the primary station, the communication control device has a line connection section that includes a transmission section and a reception section coupled to the transmission path, and the communication control device has a transmission section and a reception section of the line connection section. A delay circuit unit is connected in a subordinate manner to the transmission path, and the delay circuit unit delays the message frame and polling frame transmitted from the transmission unit by at least a time determined by the length of the polling frame, and then transmits the message frame and polling frame to the transmission path. and the receiving unit of the line connection unit starts receiving the polling frame after the transmitting unit completes sending the polling frame, and processes the message received after the polling frame as being from a secondary station. Characteristic communication control device. 2. The communication control device according to claim 1, wherein the delay circuit section has a delay time of a length corresponding to the time during which the polling frame is transmitted.