JP2557120B2 - Image transmission equipment - Google Patents

Description

The present invention relates to an image transmission device for transmitting image data using a narrow band communication line such as a general public line or wireless communication.

"Prior art" When transmitting image data using a narrow-band communication line, such as a general telephone line, the transmitting side converts the digital signal into an audio signal of about 3 KHz, and the receiving side Then, a device for performing the reverse conversion, that is, a modem is required.

Then, in the device on the receiving side, the CP that controls the device
When U processes the data, the method to receive the demodulated signal from the modem is as follows: 1) The CPU periodically polls the modem for data. 2) The modem receives 1-byte data. It is known that each time it does, it notifies the CPU of the arrival of received data by an interrupt signal, and the CPU suspends the current process and performs the receive process by a receive interrupt.

"Problems to be solved by the invention" By the way, like image transmission of videophone devices,
In applications requiring large-capacity and high-speed data transmission, the above-described received data processing method has a problem in that the processing speed of the CPU cannot keep up with the data transmission speed.

 The present invention solves such a problem.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, in a video transmission device that transmits and receives by using a communication line after converting image data into a voice band signal, the received voice band signal is received. Image data having a data length corresponding to one horizontal line or more of the image data can be stored between the demodulation unit for converting the image data into image data and the CPU for processing the demodulated image data, and A buffer memory for issuing an interrupt request to the CPU at the time when data for one horizontal line is written is provided.

[Operation] A FIFO memory is used as the buffer memory. Image data having a data length corresponding to one horizontal line or more is sequentially stored in the FIFO memory.

As a result, the CPU can collectively process the image data for one horizontal line in batch instead of the image data in 1-byte units, and the throughput of data processing is improved.

[Embodiment] Next, an example of an image transmission apparatus according to the present invention will be described in detail with reference to the drawings when applied to a videophone apparatus. As a communication line, a general public line is used.

The image to be transmitted exemplifies a case where one image is composed of 256 pixels in both the horizontal and vertical directions.

In the image transmission device shown in FIG. 1, 200A and 200B are transmission / reception sets (videophone devices) as terminal devices connected to an analog line (general telephone line) 201.

 The transmission / reception set 200A is configured as follows.

A video signal from the video camera 211 is converted into a 6-bit digital signal for one sample in the A / D converter 212, and the image data for one screen (for example, 256 × 2)
Image data for 56 pixels) is written in the image memory 209.

The 6-bit image data of each pixel read from the image memory 209 is converted into an analog signal by the D / A converter 214 and supplied to the monitor television 215.

 A CPU 206 controls the entire transmission / reception set.

The CPU 206 supplies the image data from the image memory 209 to the modulator 210 constituting the modem to perform a predetermined modulation according to a control program stored in a memory (not shown), and then sends it to the analog line 201.

Further, this CPU 206 controls writing of the received image data from the demodulator 204 constituting the modem into the image memory 209 via the FIFO memory 205 in this example which functions as a buffer memory as described later.

The FIFO memory 205 has a bit structure of 512 × 8 bits, for example, and is capable of storing 512 bytes of image data.

From the above, the image data to be transmitted is the modulator 210
Is modulated from a digital signal to an analog signal in the voice band allowed for a general telephone line, and is converted into a 2-wire 4-wire converter (NC
Analog line 201 via U) 203 and line transformer 202
Is supplied to.

The transmission signal (image data) supplied from the transmission side via the analog line 201 is the line transformer 202 and the 2-line 4
It is supplied to the demodulator 204 via the line conversion unit 203 and demodulated into 6-bit image data from the voice band signal.
It is supplied to the memory 205.

Then, the CPU 206 reads the image data from the FIFO memory 205 and sequentially writes the image data for one screen in the image memory 209.

FIG. 2 shows a detailed structure of a main part related to the present invention among the structures described above.

At the time of reception, a transmission signal is supplied from the analog line 201 to the demodulator 204 via the line transformer 202 and the two-line / four-line conversion unit 203.

The demodulator 204 demodulates 6-bit image data from the voice band signal, adds 2-bit error information, and outputs 8-bit data as data input terminals FI0 to FI0 ...
Supply to FI7. Then, the WR terminal of the FIFO memory 205 is controlled from the high level to the low level, and the FIFO memory 205 is instructed to take in the image data.

256 bytes of image data in the FIFO memory 205 demodulator 20
When it is written from 4, the half full
The flag terminal HF changes from high level to low level. Then, the FIFO memory 205 requests the CPU 206 for the interrupt service by using the interrupt request input terminal INT.

Upon receiving the interrupt request, the CPU 206 finishes the processing currently being performed by the CPU 206 and then outputs the data output terminal F of the FIFO memory 205.
Image data is taken out from O0 to FO7 via the data buffer 207. And after processing the data such as error correction,
Writing to the image memory 209 via the bidirectional buffer 208.

After the 256-byte image data corresponding to the pixel data for one horizontal line of the display screen is read from the FIFO memory 205 and written in the image memory 209, the CPU 206 ends the reception interrupt program. Then, a new 2 is added to the FIFO memory 205.
The CPU 206 performs other program processing until the image data of 56 bytes is written.

While the CPU 206 is processing the received data, new received image data is written in the FIFO memory 205, so that the received image data will not be lost in the middle.

The FIFO memory 205 stores 20 bytes of CPU data when 256 bytes of image data, which is half the 512 bytes memory capacity, is written.
Since the interrupt request is generated for 6, the CPU 206 has a time margin for data processing from the generation of the interrupt request to the writing of the maximum capacity of 512 bytes of image data in the FIFO memory 205.

Therefore, the CPU 206 does not need to immediately start the interrupt service even when it receives an interrupt request.
The length of data processing time of U206 doesn't matter much.

Received data processing is done in batches of 256 bytes, so
Interrupt processing such as register saving of the CPU 206 itself associated with the reception processing can be performed once in 256 bytes. Therefore, the efficiency of data processing is improved as compared with the conventional method in which the CPU 206 extracts the image data from the demodulator 204 each time one byte of data is received.

[Advantages of the Invention] As described above, according to the present invention, one horizontal line of image data is provided between the demodulator of the modem that modulates and demodulates the image data of the image transmission device and the CPU that processes the image data. A buffer memory having the above data length is provided.

By doing so, the CPU can process the received data in units of one horizontal pixel row, and the throughput of data processing and the like is improved.

Further, since it is not necessary for the CPU to take out the received image data immediately from the demodulator every time one byte of image data is received, it has a feature that the degree of freedom in software design is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an image transmission device according to the present invention, and FIG. 2 is a block diagram of the essential parts thereof. 200A, 200B …… Transmit / receive set 201 …… Analog line 202 …… Line transformer 203 …… 2-wire to 4-wire converter 204 …… Modem demodulator 205 …… FIFO memory 206 …… CPU 209 …… Image memory 210 …… Modem Modulator 211 …… Video camera 212 …… A / D converter 214 …… D / A converter 215 …… Monitor TV

Claims (1)

(57) [Claims] 1. A demodulation unit for converting a received voice band signal into image data, and a processing of the demodulated image data, in an image transmission device for converting image data into a voice band signal and then transmitting and receiving it using a communication line. Image data having a data length equivalent to one horizontal line or more of image data can be stored between the CPU and the like, and when the data for one horizontal line is written, the CPU is interrupted. An image transmission device characterized in that a buffer memory for making a request is provided.