JPS6333827B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving modem for a line that is slave-controlled by a microcomputer for controlling the main body of a facsimile machine or a simple data terminal.

The receiving modem of a conventional facsimile receiver or data terminal receiver consists of an electronic circuit dedicated to the modem, while an analog modem consists of an analog circuit or dedicated D, S, P (digital signal, process sensor). The digital modem is created by D, S, and P dedicated to it, and the received signal is delivered to the equipment side as a serial signal at the data rate. This requires an expensive modem, which is one reason why facsimiles are relatively expensive.

A conventional G.2 facsimile analog modem receiver is shown in FIG. 1A, in which 1 is an amplifier, 2 is an AGC amplifier, 3 is a carrier detection and keyed circuit, 4 is a bandpass filter, 5 is a carrier PLL circuit, 6 is ON/OFF for each carrier half wave
The circuit includes a synchronous detection circuit 7, a waveform equalizer 8, a low-pass filter 9, and a circuit for extracting amplitude and phase outputs from a comparator. Since it is made up of each functional circuit block as described above, it is difficult to reduce its price.

In addition, a 2400 baud modem, which is a digital modem, uses a carrier of 1800 Hz and converts 2 bits of signal into 1 wave by switching it to 4 phase waves at 1/1200 seconds each.
The phase modulation is performed using the four types of information summarized as a dibit. Figure 1 A is the receiving modem and 11 is the receiving modem.
AGC, 12 is an equalizer, 13 detects the envelope change of the arriving wave to detect the phase change point of the dive bit, 15 performs carrier reproduction, 14 detects the change in the O cross phase point at the center of the dive bit, At 16, the dibits are converted into a combined signal, which is serialized, and at 17, it is descrambled to reproduce the original signal.

As explained above, modems consist of many functional blocks and are relatively expensive.

In order to solve the complexity and high cost of these modems, the present invention minimizes the number of analog circuits and directly controls the modem with a microcomputer on the side of a device such as a facsimile machine.The purpose of this invention is to simplify and reduce the cost. Explain in detail.

FIG. 2 shows the first embodiment, in which AM.PMVSB
The case of a receiving modem will be explained. Figure 2 1 is
AMP2 is AGC, 3 is AGC control section 21
is the limiter "0" detection section, which is scanned by the microcomputer to detect the "0" cross point. If it crosses “0”, it drives the timer in the microcomputer and starts at a timing 16 times the half wave of the carrier 2100Hz, or 67.2KHz. This timing is added to the 4-bit counter 22 in the circuit, and the output is sent to the 4-bit comparator 2.
3 and the 15th or 16th interval becomes H, it means that the arriving carrier and the receiving side 2100Hz are almost synchronized. If the counter is 14 or less, it is 0.
If a cross occurs, resynchronize.
Next, check the output of this comparator every 8 or 16 times at 2100 Hz. If there is a 0 cross in the 15th section, the arriving waveform is a little early. If there is a "0" cross in the 16th section, the arriving wave is The microcomputer determines that it is too late, and instructs the 67.2kHz timer to add 1 pulse or thin out 1 pulse.If the outputs of the 15th and 16th sections are both "H", the carrier portion is output as a black signal. Since this indicates that there is no phase at all, phase tracking is not performed.
If the outputs in the 15th and 16th sections are both "L", it means that there is a synchronization error, so reset the counter and the 67.2kHz timer and redo the carrier synchronization.
Also, whether or not the phase of the arriving wave has been reversed can be determined by checking the flip-flop from the carry terminal of the counter 22.
A 4200 Hz timer is taken out and this and the output +- of the limiter 21 are set to H and L to create an exclusive OR to detect inverse phase and in-phase. Further, the amplitude of the signal can be easily extracted as an image signal (analog signal) by performing envelope detection 24 of both waves.

The first embodiment is a case of two-phase AM/PMVSB modulation, but the receiving device of a digital modem can also be directly controlled by the microcomputer of the device. For simplicity, a case of 2400 phone four-phase phase modulation (CCITT.V-26A method) will be explained.

At step 13, the envelope change point is found and the break point of the dibit is detected. Find the 0 cross point in the 1/3600 second section in the center of the davit (terminal 3
1) This causes an interrupt to be sent to the device microcontroller. Carrier 1800Hz half wave 16 times timer i.e.
Start the 57.6kHz timer and calculate up to the “0” cross in the center zone of the next dibit. In this case, the counter uses a 4-bit counter 22-B and returns to 0 every 16 times. The result of the counter is put into the comparator 23, and if 0≦～<4 or 12≦～≦16, it is determined that the phase difference is 0° or 180°, and if 4≦～<12, it is determined that the phase difference is 90° or 270°. Limiter output (32
If it is the same as the previous dibit, set it to 270° or 180°, otherwise set it to 90° or 0°.
This judgment operation is performed by the microcomputer. Figure 3A shows the timing principle and Figure 3B shows the basic circuit diagram. 22A is
A time calculation counter 31 from the boundary of the Daibit section to the beginning of the central zone becomes "H" when the central zone crosses "0". As a result, the counter 22-B is driven by the microcomputer, and when the next interrupt occurs, the results of the comparators 23A and 23B are read, and after 10 to 15 .mu.s, the lead 32 determines whether the data is positive or negative, and the die bit information is determined. Next, the dibit is put into a descrambler under microcomputer control and the result is read out.

As explained in the above example, the present invention does not use analog circuits such as carrier reproduction, but searches for the position of the "0" cross point and follows the timing digitally, or calculates the timing change, and Since these operations are executed by interrupting the device control microcomputer, it has the advantage of being extremely simple as an IC circuit. This method can also be applied to high-speed modems such as 4800bps and 9600bps.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining conventional facsimile reception, FIG. 2 is a circuit diagram of a receiving modem for explaining an embodiment of the present invention, and FIG. 3 is a circuit diagram for explaining another embodiment of the present invention. 1 is an example of a timing principle diagram and a basic circuit diagram of a digital modem receiving device.

Claims (1)

[Claims] 1 Analog or digital phase modulation modem receivers do not use a carrier regeneration circuit, but use the device's microcomputer-controlled timer, the modem receiver's limiter, "0" cross detector, timer counter, and result comparator (inside the microcomputer). 1.) A modem receiver characterized in that these operations are collectively controlled by a device microcomputer.