JPH0252537A - Carrier control system in 2-wire semiduplex communication - Google Patents

Abstract

PURPOSE:To ensure an RS interval identification of a receiver side terminal equipment MODEM by stopping the transmission of a carrier for a prescribed time exceeding the carrier delay after an internal delay compensation time elapses in the MODEM. CONSTITUTION:When a control bit Request to Send(RS) from a terminal equipment is reset at the end of data transmission, the MODEM applies internal delay compensation time setting processing and when the internal delay compensation time expires, the set processing of a non signal period is implemented. When the non signal period is finished, the RS ON monitor processing starts and the set of RS are awaited, and when the RS reaches ON, the data transmission is executed, The length of non signal period set in succession to the internal delay compensation time is decided to be a time sufficiently to turn off a Carrier Detected, then the end of each data sent continuously is detected surely by a MODEM at the reception terminal equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] This invention relates to a modem carrier control method for ensuring data reception by a receiving terminal in two-wire half-duplex communication.

The purpose is to ensure that the receiving modem can detect the end of each successive data transmission.

In two-wire half-duplex communication, the modem provides a no-signal period in which carrier transmission is stopped for a certain period of time following the internal delay compensation time after data transmission is completed, and the receiving modem turns off the carrier detection status bit. It was configured to give sufficient time.

(Industrial Application Field) The present invention relates to a data communication system, and particularly to a modem carrier control system for ensuring data reception by a receiving terminal in two-wire half-duplex communication.

[Conventional technology]

Fourth, the configuration of a conventional two-wire half-duplex communication system is shown.

In FIG. 4, l is terminal A, 2 is terminal B, 3 and 4 are modems, and 5 is a line.

The interface between each terminal and the modem consists of transmit and receive data, as well as control bits and status pins.

Modem 3 or 4 converts parallel format transmission data output from terminal 1 or 2, respectively, into serial format,
It modulates the carrier, sends it out to line 5, and transmits it to the modem of the other party's terminal.

The modem 3 or 4 that has received the modulated signal demodulates the data, converts it into parallel received data, and causes the respective terminal 1 or 2 to read the data.

FIG. 5 shows a control sequence for the interface between each terminal and the modem when data is transmitted from terminal A to terminal B.

FIG. 5(a) shows the ink face to the terminal and the RS
(RequesLto 5end) is a control bit that requests the modem to prepare for transmission from the terminal, cs (C1
earth.

5end) is a status bit that notifies the line transmission readiness state from the modem to the terminal, and SD (Send Dat
a) represents transmission data. Note that T in R3 is an off period provided in case of continuous data transmission, and RS
called an interval.

FIG. 5(b) shows the interface of terminal B.

CD (Carrier Detected) is a status bit RD that notifies the terminal of carrier detection from the modem.
(To+adData) represents received data.

FIG. 6 shows the internal sequence of the modem. When data transmission is finished and R3 is turned off, the modem detects this, stops transmitting the carrier, and notifies the terminal of the off state of C3. If the terminal has prepared the next data to send,
After the RS interval T, R3 is turned on again.

However, the modem does not monitor RS-on immediately after RS-off, but waits until the modem's internal control state stabilizes by allowing an appropriate internal delay compensation time, and then monitors R3 (indicated by the Wait state). I have to. When RS on is detected here, carrier transmission is restarted and C
Turn on 8.

[Problem to be solved by the invention]

In conventional two-wire half-duplex communication, the RS interval provided by the transmitting terminal after data transmission is sometimes relatively short. In this case, the receiving terminal's modem looks at R3 after the internal delay compensation time has elapsed, so the carrier may appear to be continuing and the CD may not be turned off. A similar thing happened when the carrier transmission was delayed due to the influence of the line, and the carrier could not be disconnected by the receiving terminal's modem. In these cases, as shown in FIG. 7, since the next data is transmitted with the CD on, the primary reception timing becomes abnormal and an error occurs in the received data RD.

Moreover, such a situation is particularly likely to occur when terminals with various characteristics are connected at multiple points because their RS intervals are different.

This problem can be solved by lengthening the RS interval on each of the five terminals, but since the terminal usually does not know how long it should be, it has been difficult to deal with it in practice.

An object of the present invention is to enable the receiving modem to reliably detect the end of each continuously transmitted data.

[Means to solve the problem]

The present invention enables a receiving terminal to reliably identify the RS interval by stopping carrier transmission within the modem for a certain period of time exceeding the carrier delay after the internal delay compensation time has elapsed. .

FIG. 1 is a diagram explaining the principle of the present invention.

In the figure, 1 is terminal A, 2 is terminal B, 3.4 is a modem, and 5 is a line. Note that the flow within the modem 3 in FIG. 9 shows the control sequence at the time of data transmission, and for simplicity, shows the control state from the end of data transmission to the transmission of the next data.

When RS off is detected in the RS off monitoring process (2).

Perform the internal delay compensation time setting process described in (2).

■When the internal delay compensation time times out.

■Stop carrier transmission.

Setting processing for a no-signal period (hereinafter referred to as NTE) is performed. ■
The length of the NTE is determined to be sufficient time for the receiving terminal's modem to turn off the CD.

When the NTE (2) is completed, the RS ON monitoring process (2) is started and waits for R3 to be turned on.

When R3 is turned on in (2), data transmission is executed.

[Operation] According to the present invention, the terminal does not need to consider the characteristics of the other terminal or the carrier delay on the line regarding the length of the RS interval, and the modem automatically inserts the NTE.
System changes such as adding more terminals using multi-points become easier.

[Example] The present invention will be explained in detail with reference to FIGS. 2 and 3.

FIG. 2 shows the internal sequence of a modem according to two embodiments of the present invention. When the control bit R3 from the terminal turns off due to the end of data transmission, the modem starts a turn-off sequence and turns off C3 to turn off the terminal. respond to

The turn-off sequence is a period in which R3 monitoring is not performed, and has a length equal to the sum of the internal delay compensation time Td and the NTE time tn.

After the turn-off sequence is completed, it shifts to the Wait state and starts R3 monitoring.

FIG. 3 shows an example of the operation of the modem when transmitting data.

As shown in the figure, C8 is turned on/off following the turning on/off of R3. The carrier is stopped after RS off detection, but R3 monitoring is not performed until the end of NTE, so even if the terminal turns on R3 for the next data transmission, NTE
There is no carrier transmission during this period, thus ensuring no-signal detection at the receiving modem and allowing the CD to cool off.

(Effects of the Invention) According to the present invention, there is no need to consider the length of the RS interval depending on the characteristics of the nine lines or the other terminal in a system where a large number of terminals are multi-point connected and data communication is performed. Since it can be easily handled by just changing the function slightly, it is possible to improve the reliability of data transmission at low cost.

■: Internal delay compensation time setting process ■: No signal period (NTE) setting processing ■: RS on exaggeration processing

Claims (1)

[Claims] In two-wire half-duplex communication, modems (3, 4) provide a no-signal period in which carrier transmission is stopped for a certain period of time following an internal delay compensation time after data transmission is completed, and the receiving modem enters a carrier detection state. A carrier control method in two-wire half-duplex communication characterized by providing sufficient margin time to turn off bits.