JPS6126344A - Modem - Google Patents

Abstract

PURPOSE:To easily restore from an out-of-synchronism state, by providing a function which performs self-synchronization under conditions where no synchronizing signal is transmitted from the MODEM of other stations. CONSTITUTION:When a transmission request is made from a terminal device 1, a transmission clock is selected by a reception/transmission selecting circuit 2 and a synchronizing signal is generated through a synchronizing signal generating circuit 9 and sent to the MODEM11 of another station through a transmission selecting circuit 7. The signal transmitted from the MODEM11 is supplied to a demodulator circuit 8 through a reception selecting circuit 15, demodulated by the clock signal of a received clock synchronizing circuit 16, and sent to the terminal device 1. When an out-of-synchronism state occurs for some reason, an out-of-synchronism signal is outputted from the demodulator circuit 8 and a synchronism restoring sequence circuit 10 performs a prescribed sequence operation for restoring synchronism. Namely, the circuit 10 performs the sequence operation until obtaining the clock at the receiving side from the transmitting side signal in the marked period and successing in establishment of synchronism after the detection of the out of synchronism.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a modem used for data communication between a computer and a terminal within or outside the premises, particularly for local area work.

[Description of prior art]

Asynchronous modems are often used for data communication by connecting computers and electronic devices such as terminals and personal computers, but due to reliability and communication speed issues, synchronous modems are often used. is also used. This synchronous modem has the disadvantage that the circuit structure is complicated and expensive in order to cope with out-of-synchronization caused by noise or other causes.

In particular, in the case of the multi-drop method (see Figure 1), in which multiple terminal devices are connected to one line, each terminal device connected to the communication line is in a different state, so If one of the devices goes out of synchronization, it is necessary to synchronize the device itself without interfering with the 1ffl transmission of other devices in use. However, conventional modems use a method in which the local modem receives a synchronization signal transmitted from the other station's modem, and synchronizes the own station's modem accordingly. can be self-synchronized, the synchronization function is: L; L is 1 minute, 1 is not large - 0
[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide a synchronization signal generation function for synchronizing modems of other stations, and a synchronization signal generation function for synchronizing modems of other stations. It has a self-synchronization function upon receiving a synchronization signal, as well as a function to perform self-synchronization when no synchronization signal is transmitted from the modem of another station, providing a highly reliable (and economical modem with a simple circuit configuration) There is a particular thing.

[Structure of the invention]

A modem according to the present invention is a modem equipped with a means for using a self-synchronizing signal to recover synchronization loss that occurs during demodulation of a received signal using a self-synchronization signal, and the modem is equipped with a means for recovering synchronization loss that occurs during demodulation of a received signal using a self-synchronization signal, and the modem is configured to recover a synchronization clock from a mark period of the reception signal when the loss of synchronization is detected. The feature is that synchronization is recovered by generating a synchronization signal synchronized with the generated synchronization signal in its own modem. A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, in which portions that characterize the present invention are surrounded by broken lines. In the figure, 1 is a combiator or a terminal, and 1 is a combiator or a terminal. S-232
It is connected to the modem according to the present invention via a C serial port. An R3 (transmission request) terminal and a C3 (transmission enabled) terminal in this boat are connected to a reception or transmission clock selection circuit 2. The Txc (transmission clock) terminal is also connected to a transmission frequency synchronization circuit 5 that synchronizes the transmission frequency in cooperation with the output of a clock frequency division selection circuit 4 that selectively divides the output of the clock oscillator 3. Ru. Txd
(The transmission data terminal is connected to the modulation circuit 6, and the take modulated by the modulation circuit 6 is supplied to the transmission selection circuit 7. Also, the Rxc (reception clock) and Rxd (reception data) terminals are connected to the demodulation circuit. Connected to 8].-
The above-described reception or transmission clock selection circuit 2 selectively switches between a clock based on the reception signal 8 and a clock based on the transmission signal, and supplies a signal for synchronization to the synchronization signal generation circuit 9.

Further, the receiving or transmitting clock selection circuit 2 is supplied with the output of a synchronization recovery sequence circuit 10 that performs a synchronization recovery sequence operation in response to an out-of-synchronization signal generated by the 19th tone circuit 8. Reference numeral 11 denotes a remote station modem connected to a computer or a terminal, and is connected to a voltage/current conversion circuit 13 and a current/voltage conversion circuit 14 via a four-wire loop line 12. The output of the current/voltage conversion circuit 14 is supplied to the demodulation circuit 8 via a selection circuit 15 for selecting a synchronization signal and a reception clock synchronization circuit 16 for synchronizing the reception frequency.

FIG. 3 shows a pimmy pattern applied to a modem according to the present invention. Immediately, the state of the mark (
Indicated by A in the figure. Part B is in synchronization (an example of a bit pattern of No. 8 is shown), and the modem according to the present invention repeats the same 1 and 1 deviation (18 times) in the state of this mark.

[Action of the invention]

Hereinafter, the operation of the modem according to the present invention will be explained with reference to FIG. In the figure, when a transmission request is generated from a computer or terminal I, a transmission clock is selected by a reception or transmission clock selection circuit 2, and a synchronization signal generation circuit 9
A synchronizing signal is issued via the transmission selection circuit 7 and supplied to the voltage/current conversion circuit 13, whereupon the current is converted and sent to the other station modem 1 connected to the computer or terminal.
1. Then the computer or lJfMl
Transmission is started from the other station modem 11 connected to the terminal,
The signal voltage-converted by the current/voltage conversion circuit 14 is supplied to the demodulation circuit 8 via the reception selection circuit 15, demodulated by the demodulation circuit 8 based on the clock signal from the reception clock synchronization circuit 16, and converted into a reception take. The reception clock is detected and the reception data is sent to the Rxd (reception data) terminal.
Further, the reception f11 clock is supplied to the Rxc terminal. The operation described above is similar to that of the known circuit configuration.

Next, a case will be described in which synchronization occurs when a modem is used in a multi-drop system and, for example, the power of some terminal equipment is suddenly turned on. That is,
When an out-of-synchronization occurs, an out-of-synchronization signal is generated as an output of the demodulation circuit 8, causing the synchronization recovery sequence circuit 10 to perform a sequence operation for recovery of synchronization. Here, the reception or transmission clock selection circuit 2 switches the clock to the reception clock, and outputs a synchronization signal synchronized with the reception clock obtained by detecting the mark signal from the reception clock synchronization circuit 16 (bit B in FIG. 3). pattern) is sent out from the synchronization signal generation circuit 9, this synchronization signal is selected by the reception selection circuit 15 and supplied to the demodulation circuit 8, and the synchronization is restored. During this time, a transmission cutoff signal is sent to the transmission selection circuit 7 to cut off and protect the transmission line. This synchronization sequence is repeated until the out-of-synchronization signal disappears.

〔Effect of the invention〕

As described above, the modem according to the present invention has a synchronization signal generation function for synchronizing other station modems, and a self-synchronization function by receiving a synchronization signal transmitted from another station modem.
It also has a function to perform self-synchronization with its own modem when synchronization is lost in a state where no synchronization signal is transmitted from the modem of another station. That is, after detecting out-of-synchronization, the clock on the receiving side is obtained from the transmitting-side signal during the mark period, and the sequential operation for synchronization recovery is performed until synchronization is successfully achieved, so recovery from out-of-synchronization is easy and reliable. This has the effect of providing an economical modem with a high cost and a simple circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a multi-trot block system, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a diagram showing a bit pattern applied to a modem according to the present invention. Explanation of symbols■-Computer or terminal, 2-Reception or transmission clock selection circuit, 5-Transmission frequency synchronization circuit, 7-Transmission selection circuit, 8-Demodulation circuit, 9-Synchronization signal generation circuit, 10-
Synchronization recovery sequence circuit, 11-other station modem connected to computer or terminal, 12-loop line, 13
- Voltage / current conversion circuit, 14 - Current / T"J voltage conversion circuit, 15 - Reception selection circuit, 16 - Reception clock synchronization circuit, 17 - Own station modem

Claims (2)

[Claims] (1) A modem equipped with means for recovering synchronization loss that occurs during demodulation of a received signal using a self-synchronization signal, the modem having a means for recovering synchronization loss that occurs during demodulation of a received signal using a self-synchronization signal, the modem having a clock synchronized with the reception signal from the mark period of the reception signal when the loss of synchronization is detected. A modem that performs self-synchronization using a synchronization signal detected and transmitted. (2) A circuit is provided for selectively generating a clock based on a received signal and a clock based on a transmitted signal, and the clocks are switched and synchronized when an out-of-synchronization is detected. The modem described in item 1.