JP2984573B2 - Half-duplex modem - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a half-duplex modem and, more particularly, to a half-duplex modem connected to a two-wire dedicated line and transmitting data in a half-duplex system.

[0002]

2. Description of the Related Art Conventionally, this type of half-duplex modulation / demodulation apparatus controls on / off of a carrier for switching between transmission and reception. At the moment when the carrier is turned off, an extra bit (pseudo data) caused by an excessive phenomenon is generated on the receiving side. Occur. Since this pseudo data is input to the terminal side and results in a data error,
A circuit for suppressing this is provided.

FIG. 3 is a block diagram showing a configuration in a conventional example, and FIG. 4 is a timing chart of each signal in FIG.

In FIG. 3, modems 6 and 7 are devices having the same configuration and mutually transmit and receive data signals via a two-wire dedicated line 8. Transmission and reception are controlled by turning the carrier on and off. That is, the DC transmission signals from the terminals 9 and 10 are modulated by a carrier and converted into AC signals,
Modulation / demodulation units 65 and 75 having a function of interrupting the carrier.
An off-delay section 61, 71 for delaying the turning off of the transmission request (RS) signal for a predetermined time; and an SD clamp section for clamping the transmission data (SD) signal from the terminals 9, 10 to the off-delay time Z polarity of the RS signal. 62, 72; RD delay units 64, 74 for delaying the modem reception data (MRD) signal from the modem unit for a predetermined time; and reception data (RD) immediately after the modem carrier detection (MCD) signal is turned off.
RD clamp units 65 and 75 for clamping a signal to Z polarity
It is composed of

Next, the operation will be described with reference to FIGS. The description will be made on the direction in which the data signal is transmitted from the terminal 9 and received on the terminal 10 side, but the same applies to the opposite direction. The terminal 9 turns on the RS signal 131 before the transmission of the SD signal 133 starts. Upon detecting that the RS signal is on, the modem 65 starts transmitting the carrier, and the modem transmission data (MSD) signal 137 from the SD clamp unit 62.
And transmits the modulated data to the other party's modem 75 through the dedicated line 8 as an analog signal.

[0006] When detecting the carrier, the modem 75 detects M
While the CD signal 145 is turned on, the modulation data of the received analog signal is demodulated and the MRD signal 148 is sent to the RD delay unit 74. RD delay section 74 is MRD
After the signal 148 is delayed for a certain time, the RD clamp unit 75
Send to RD clamp unit 75 that has detected MCD ON
Releases the Z clamp of the MRD signal 148 and sends the received data to the terminal 10 as the RD signal 144.

[0007] After the transmission of the SD signal 133 is completed, the terminal 9 sets R
The S signal 131 is turned off. The off-delay section 61 causes the RS signal 131 to be on-clamped for a certain time, thereby
Even after the S signal is turned off, the carrier transmission and modulation of the modulation / demodulation unit 65 are continued for a certain period of time. During this time, the SD clamp unit 62
The D signal 137 is sent to the modem 65 with the Z polarity.
The modulator / demodulator 65 modulates the Z polarity and continues to transmit the modulated data to the partner modem 7 via the dedicated line 8.

[0008] The modulation / demodulation unit 75 demodulates the modulated data and sends an MRD signal 148 of Z polarity to the RD delay unit 74. The RD delay unit transmits the MRD signal 148 to the RD clamp unit 75 after delaying it by a predetermined time. Since the MCD signal 148 is ON, the RD clamp 75
RD of Z polarity with Z clamp of signal 148 released
The signal 144 is sent to the terminal 21. After a lapse of a predetermined time, the off delay unit 61 turns off the MRS signal 136. The modulation / demodulation unit 65 that has detected this RS off stops transmitting the carrier. When the modem 75 detects that the carrier has been disconnected, MC
The D signal 148 is turned off, but there is a slight delay before this detection. RD clamp unit 7 that detects MCD signal off
5 Z-clamps the MRD signal 148. This clamp suppresses the transmission of the extra bits generated by the modem 65 before and after the carrier disconnection to the terminal side.

The MRD signal 148 is supplied to the RD delay unit 7
The purpose of the delay in the MCD signal 14 is as described above.
This is to absorb a delay in clamping of the MRD signal due to a delay when the switch 8 is off. The purpose of giving the Z-polarity off delay to the MSD 137 is that the MCD signal
This is because the RD signal is clamped in the time zone of the Z polarity when clamping, in order to prevent the clamping from affecting the actual data.

[0010]

In the conventional apparatus, the MRD signal is clamped by the MCD signal in order to remove the extra bit in this manner. Since the RD delay time is required, and the data transmission time adds this delay time to the actual data transmission time, there is a problem that the transmission efficiency of the transmission path is deteriorated.

[0011]

According to the present invention, there is provided a half-duplex modem, comprising: an off-delay section for receiving a transmission request signal (RS signal) from a terminal and delaying a falling portion thereof for a predetermined time and outputting the signal; When the rising bit of the transmission data signal (SD signal) from the terminal is set to the A polarity by the signal, and the subsequent bit continues the Z polarity by a predetermined number of bits, the polarity of the next bit is inverted and the RS bit is delayed. A bit inversion transmission unit that clamps and outputs a corresponding falling portion to the Z polarity, transmits a transmission carrier with an output signal of the off-delay unit, and simultaneously modulates an output signal of the bit inversion transmission unit into an analog signal and transmits the transmission carrier. A modulation / demodulation unit for transmitting the signal to the transmission line, and a modulation / demodulation unit for receiving the analog signal from the transmission line and demodulating and outputting the digital signal. A carrier detection signal (CD signal) which turns on when the A signal of the rising bit of the digital signal is input and detects the A polarity of the rising bit of the signal and turns off when a predetermined number of consecutive Z polarities of the falling portion are counted; A bit inversion receiving unit that outputs a reception data signal (RD signal) obtained by inverting the polarity of the next bit when the predetermined number of bits whose Z polarity is counted by the bit inversion transmission unit continues, A CD clamp unit for controlling transmission to a terminal by the CD signal.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a circuit configuration of this embodiment. FIG. 2 is a timing chart of each signal in FIG.

In FIG. 1, half-duplex modems 1 and 2 receive data signals and control signals from terminals 4 and 5, respectively.
Data signals are mutually transmitted and received via the line-type dedicated line 3. The internal configurations of the half-duplex modems 1 and 2 have exactly the same configuration. That is, the modulation / demodulation units 13 and 23 that perform data transmission and perform half-duplex communication with intermittent carriers
And transmission data (S
D) Signals 103 and 113 or modem reception data (M
RD) polarity inversion control units 12 and 22 for performing polarity inversion control of the bits of the signals 108 and 118;
12 and the MRD signals 108 and 118 from the modem
An RD clamp unit 14, which clamps to a polarity (logical value 1),
24.

Next, the operation will be described with reference to FIGS. First, the terminal 4 on the data transmitting side turns on the RS signal 101 to the half-duplex modem 1, and then transmits the SD signal 103. When the polarity inversion control unit 12 detects that the RS signal is on, it sends out the A polarity (logical value 0) to the 1-bit modulation / demodulation unit 13. Subsequently, the SD signal 103 transmitted is monitored, and if the Z polarity continues for 4 bits, the next 1 is output.
After the polarity is inverted, the bit is transmitted to the modulation / demodulation unit 13. As a result, the MSD signal transmitted to the modulation / demodulation unit 15 is prevented from having a continuous Z polarity. When detecting the RS signal ON, the modulation / demodulation unit 13 starts carrier transmission, and the polarity inversion control unit 1
2 is modulated into an analog signal on the dedicated line side.

The modem 2 receives this analog signal through the dedicated line 1. The modulator / demodulator 23 receives the received data M
The signal is demodulated into an RD signal 118 and sent to the polarity inversion control unit 22. The polarity inversion control unit 22 monitors the MRD signal and turns on the CD signal 115 when detecting one bit of the A polarity. When the Z polarity continues for 4 bits, the polarity of the next 1 bit is inverted. As a result, the data whose polarity has been inverted by the polarity inversion controller 12 on the transmission side is restored. The RD clamp unit 24 that has detected the CD signal ON cancels the Z clamp of the MRD signal 118 and sends the received data MRD to the terminal 21 as an RD signal.

When data transmission is completed, the terminal 4 turns off the RS signal 101 to the half-duplex modem 1. At this time, the off-delay unit 11 keeps the RS signal 101 on-clamp for a certain period of time, so that the carrier transmission and modulation of the modem unit 13 are continued for a certain period of time even after the RS is turned off. During this time, the polarity inversion control unit 12 keeps sending the Z polarity to the modulation / demodulation unit 13.

The polarity inversion control section 22 on the receiving side monitors the MRD signal 118, and turns off the CD signal 115 when detecting 48 consecutive Z-polarity bits. The RD clamp unit 24 that detects the CD signal off clamps the MRD signal 118 to Z polarity. This clamp suppresses the extra bit due to the harmonic component generated by the modulation / demodulation unit 23 immediately after the carrier disconnection from flowing to the terminal 5 side.

The purpose of the bit inversion of the Z polarity after four consecutive bits is to detect the CD signal off by detecting the S signal on the transmitting side.
This is because the continuity of the Z polarity of the D signal is interrupted, and the 48 consecutive bits at the time of detecting the CD signal OFF are the number of bits determined with a margin for the 4-bit continuation. Further, the off-delay time of the SD signal on the transmitting side is set to a long time necessary for detecting these 48 bits.

[0020]

As described above, the half-duplex modem according to the present invention clamps the RD signal to suppress the extra bit. This is done by counting only bits. Therefore, there is no need to delay the RD signal itself, and the off-delay time of the RS signal need only be slightly longer than 48 bits, so that the overall delay time can be reduced and the transmission efficiency can be improved. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a timing chart of each signal in FIG. 1;

FIG. 3 is a block diagram of a conventional example.

FIG. 4 is a timing chart of each signal in FIG. 3;

[Explanation of symbols]

 5 Dedicated line 3,4 Terminal 1,2 Half-duplex modem 11,21 Off delay unit 12,22 Polarity inversion control unit 13,23 Modulation / demodulation unit 14,24 RD clamp unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-73828 (JP, A) JP-A-2-134036 (JP, A) JP-A-64-20747 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04L 5/16 H04L 29/00

Claims (1)

(57) [Claims] 1. A half-duplex modem for performing half-duplex communication by carrier control via a two-wire transmission path, receiving a transmission request signal (RS signal) from a terminal and delaying a falling portion thereof by a predetermined time. An output off-delay section;
When the rising bit of the transmission data signal (SD signal) from the terminal is set to the A polarity by the S signal, and the subsequent bit continues the Z polarity by a predetermined number of bits, the polarity of the next bit is inverted and the delay portion of the RS signal is delayed. A bit inversion transmission unit for clamping and outputting a falling portion corresponding to Z-polarity, outputting a transmission carrier with an output signal of the off delay unit, and simultaneously modulating an output signal of the bit inversion transmission unit to an analog signal and transmitting the transmission signal. A modulator / demodulator for transmitting the signal to the transmission line on a carrier; a modulator / demodulator for receiving the analog signal from the transmission line, demodulating the signal into a digital signal, and outputting the digital signal; A carrier detection signal that turns on when the A polarity is detected and turns off when the predetermined number of bits of the continuous Z polarity at the falling edge are counted. Bit inversion for outputting a (CD signal) and a reception data signal (RD signal) in which the polarity of the next bit is inverted when the digital signal continues the predetermined number of bits whose Z polarity is counted by the bit inversion transmission unit. A half-duplex modem, comprising: a receiving unit; and a CD clamp unit that controls transmission of the RD signal to a terminal by the CD signal.