JPH04310759A - Thermal printer - Google Patents

Abstract

PURPOSE:To provide a simple circuit structure without duplex configuration of memory by employing a dynamic RAM memory having a page memory, in a printer wherein a heat generating resistor of a thermal head is energized for a time of integer multiple of a unit time so as to output images including intermediate tone. CONSTITUTION:A frame memory 1' is constituted of a dynamic RAM memory capable of reading out a page mode. A read out control circuit 2' outputs a line address signal RL. In this state, a RAS signal designates a line i of the memory 1' and addresses of each picture element of 1 line are outputted successively. In accordance with a CAS signal synchronizing with this, image data of each picture element of the line i are outputted to a comparator 4 successively so as to be compared with a count value of a counter 5. When the outputting of the image data of each picture element in the line i is completed, the line i is designated again so that the image data is read out. This is repeated for the number of density gradations so that image of the line i is outputted and a next line process starts.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer that outputs an image including halftones by energizing a heating resistor of a thermal head for an integral multiple of a unit time.

0002

[Prior Art] As a method for expressing halftones in thermal printers, there are methods that control the amount of current per unit time that flows through the heating resistor of the thermal head, and methods that control the amount of current per unit time that is constant. A method of controlling the energization time is adopted in the present invention, and as one of the methods of controlling the energization time, for example, the following method is adopted.

FIG. 3 is a circuit block diagram showing an example of a conventional method for controlling image density by controlling the energization time. The conventional technology will be explained below with reference to this figure. Image data for one image is stored in a frame memory 1 consisting of a dynamic RAM memory, and an address ADD of image data for one pixel in the frame memory, a RAS signal, and a CAS signal are sent to the frame memory 1 from a readout control circuit 2. As a result of the input, image data for one pixel consisting of, for example, 8 bits is output from the frame memory 1 and input to the line memory 3. The line memory 3 is a memory that stores image data for one line (for example, 512 pixels), and while the readout control circuit 2 instructs the address ADD of each pixel in one line, the RAS signal and CAS are
As a result, image data corresponding to each pixel in one line is sequentially output from the frame memory and stored in the line memory 3.

When one line of image data is stored in the line memory 3, reading of the image data from the frame memory 1 is temporarily interrupted, and the one line of image is output as follows. be done. line memory 3
From there, one line of accumulated image data is sequentially output pixel by pixel and input to the comparator 4. Further, the counter 5 is a counter that is incremented every time all one line of image data is output from the line memory 3, and this count value is also input to the comparator 4.

This comparator 4 compares the image data corresponding to each input pixel with the count value, and when the image data is greater than or equal to the count value, the data is sent to the shift register 6a in the head unit 6. Outputs a pulse signal. By repeating this for one line for each image data that is sequentially input, the shift register 6a has '1' for pixels whose image data is larger or equal to the count value in one line, and '0' for other pixels. '
A bit pattern is formed. When the bit pattern is formed in the shift register 6a in this way, the heating resistors H0, H1,..., H51 are lined up by the number of pixels for one line.
1, the heating resistor corresponding to the '1' bit in the shift register 6a is energized for a unit time, thereby forming a density pattern corresponding to the unit density on the thermal paper.

Next, the count value of the counter 5 is incremented by 1 and input to the comparator 5, and the image data for one line already stored in the line memory 3 is incremented by 1.
The signal is output again for each pixel and input to the comparator 4, a bit pattern is formed in the shift register 6a in the same manner as above, and the heat generating resistor corresponding to the '1' bit is energized again.

By repeating the above operation for the number of density gradations (for example, 64), one line of image stored in the line memory 3 is recorded on the thermal paper. When this one line of repetition (for example, 64 times) is completed, the next one line of image data is transferred from frame memory 1 to line memory 3, and the newly transferred one line of image data is transferred in the same way as above. The image is outputted onto thermal paper, and by repeating the above steps, an image having, for example, 64 density gradations is outputted onto the thermal paper.

[0008]

[Problems to be Solved by the Invention] With the above configuration, it is possible to output an image having halftones by controlling the energization time to the heating element resistors H0, H1,..., H511, but the circuit configuration is complicated. In particular, in addition to the frame memory 1, a line memory 3 for storing one line of image data is provided, resulting in double memory. This is because reading from the frame memory 1 is slow, so one line of image data is transferred to the line memory 3 and the one line of image data is used repeatedly (for example, 64 times).

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a thermal printer with a simple circuit configuration that does not require duplication of memories.

0010

[Means for Solving the Problems] A thermal printer of the present invention for achieving the above object includes a dynamic RAM memory having a page mode in which image data for an image is stored, and one line each from the dynamic RAM memory. a readout control circuit that repeatedly reads image data corresponding to the number of density gradations; and a gradation control circuit that rewrites and outputs gradation data representing each density gradation each time one line of image data is read from the dynamic RAM memory. a data generator; each time one pixel worth of image data is read out from the dynamic RAM memory;
a comparator that compares the image data read from the AM memory and the gradation data output from the gradation data generator and outputs a pulse signal depending on the magnitude of the values of the image data and the gradation data; and a thermal head section including a register for storing one line of the pulse signal.

[0011]

[Operation] In recent years, dynamic RAM memories have appeared that are capable of page mode reading, which allows one line of data to be read out at high speed. The present invention has been made with this in mind. That is, the present invention is configured so that the image data of each line is repeatedly read out from the dynamic RAM memory, for example, 64 times, thereby eliminating the need for a line memory that stores image data for one line. , the circuit configuration is simplified.

0012

[Examples] Examples of the present invention will be described below. Figure 1
1 is a circuit block diagram of a thermal printer according to an embodiment of the present invention. FIG. In this figure, blocks having the same functions as the blocks in the conventional circuit configuration (FIG. 3) described above are given the same numbers as those in FIG. 3, and their explanations will be omitted.

The frame memory 1' shown in FIG. 1 is composed of a dynamic RAM memory capable of page mode reading, and the read control circuit 2' sends a signal to the frame memory 1' to perform page mode reading. will be sent. FIG. 2 is a time chart of signals input from the read control circuit 2' to the frame memory 1'.

While the read control circuit 2' outputs the address signal Ri for a certain line (line i), the RAS signal falls, thereby specifying the line i of the frame memory 1'. Here, this RAS signal is held low, and the addresses C0, C1, and
..., while sequentially outputting C511, CAS
Bring down the signal repeatedly. As a result, image data for one line of line i is sequentially output for each pixel. This output image data is directly input to the comparator 4,
Comparison processing is performed in the same manner as in the conventional example described above.

When the image data of each pixel in line i is output across the entire line i, line i is designated again and the image data of each pixel in line i is read out again, and this is repeated, for example, 64 times. Line i on the thermal paper
The related image is output, and then the process moves to line i+1. By using a dynamic RAM memory having a page mode as the frame memory 1 in this manner, image data can be repeatedly read out at high speed, thereby making it possible to omit a line memory and simplifying the circuit configuration.

[0016]

Effects of the Invention As explained above, the thermal printer of the present invention uses a dynamic RAM having a page mode.
The inclusion of memory simplifies the circuit configuration, leading to cost reductions.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of a thermal printer according to an embodiment of the present invention.

FIG. 2 is a time chart of signals input to a frame memory from the read control circuit shown in FIG. 1;

FIG. 3 is a circuit block diagram showing an example of a conventional method for controlling image density by controlling energization time.

[Explanation of symbols]

1, 1’ Frame memory 2, 2' Read control circuit 3 Line memory 4 Comparator 5 Counter 6 Head part

Claims (1)

[Claims] 1. A dynamic RAM memory having a page mode in which image data for one image is stored; a readout control circuit that repeatedly reads image data for each line by the number of density gradations from the dynamic RAM memory; a gradation data generator that rewrites and outputs gradation data representing each density gradation every time one line of image data is read from the dynamic RAM memory; and a gradation data generator that outputs one pixel worth of image data from the dynamic RAM memory. is 1
Each time the image data is read out, the image data read out from the dynamic RAM memory and the gradation data output from the gradation data generator are compared, and depending on the magnitude of the values of the image data and the gradation data, What is claimed is: 1. A thermal printer comprising: a comparator that outputs a pulse signal; and a thermal head section that includes a register that stores one line of the pulse signal.