JPS6344231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a dot pattern computer which allows dot pattern data to be written into a dot pattern memory using a display character code memory.
This relates to a method for writing data into memory.

FIG. 1 shows part of a conventional display device, in which 1 is an address counter, 2 is a display character code memory, 3 is a latch, 4 is a multiplexer,
5 each indicate a dot pattern memory composed of RAM.

Address counter 1 indicates the address of the display character code memory, and the character code of the character to be displayed is written in the address specified by address counter 1. The display character code memory 2 stores character codes for one screen to be displayed. Latch 3 stores external address information. Multiplexer 4 is
When reading the dot pattern from the dot pattern memory 5, select the data to be read from the display character code memory 2, and select the dot pattern.
When writing external dot pattern data to memory 5, select the data in latch 3 and use the selected data as address information to write the dot pattern data.
Send to memory 5. The dot pattern memory 5 stores dot pattern data of a plurality of characters. The starting address of the area where one character of dot pattern data is stored is uniquely determined by the character code. One character is represented by, for example, 16×16 dots, and one word of the dot pattern memory 5 is composed of, for example, 2 bytes.

Address counter 1 actually consists of a row counter and a digit counter. The combination of the contents read from the display character code memory 2 and the contents of the raster counter becomes the actual read address of the dot pattern memory 5. The line counter indicates the line on the display of the character to be displayed, and the column counter indicates the column position of the character within the line. The raster counter indicates the raster number when displaying one line of characters. The contents of the digit counter are incremented by 1 when a predetermined number of dots are displayed, and the contents of the raster counter are incremented by 1 when the digit counter outputs a offset. The contents of the row counter are incremented by 1 when the raster counter outputs a carry.

Since the dot pattern memory 5 is composed of RAM, its contents are lost when the power is cut off. Therefore, it is necessary to write new data into the dot pattern memory 5 when the power is turned on. When writing data to the dot pattern memory 5, the main unit sends external address information and external dot pattern data to the display device, and the display device selects the external address information using the multiplexer 4. Then, the external dot pattern data is written to the address of the pattern memory 5 specified by the external address information.

In this way, the conventional device as shown in FIG.
In order to write data to the dot pattern memory 5, a latch 3 and a multiplexer 4 are required, which has the disadvantage that the amount of hardware increases by this amount compared to a case where the dot pattern memory 5 is composed of a ROM or the like. It shows.

The present invention eliminates this drawback and includes:
It is an object of the present invention to provide a method for writing data to a dot pattern memory, which allows data to be written to the dot pattern memory without providing multiplexers or latches as described above. Therefore, the data writing method to the dot pattern memory of the present invention requires a display character code memory in which character codes are stored, an address counter that specifies the address of the display character code memory, and a random access memory. A display device comprising a dot pattern memory composed of a memory, and in which dot pattern data is read from an address in the dot pattern memory specified by a character code read from the display character code memory. When writing dot pattern data to the dot pattern memory, write the character code to the display character code memory while updating the address counter using an external clock signal from outside the display device, and then write the character code to the display character code memory. Clear the address counter with an external clear signal, then read the character code from the display character code memory while updating the address counter with an external clock signal, and display the dot pattern specified by the read character code. This method is characterized by writing external dot pattern data to memory addresses. Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 2 is a block diagram of one embodiment of the present invention. In FIG. 2, 6 indicates an AND circuit, and 7 indicates an OR circuit. Note that the same reference numerals as in FIG. 1 indicate the same parts. The AND circuit 6 prohibits the address counter from being updated by the clock source on the display device side, and the dot pattern memory 5
When data is written to, the AND circuit 6 is forcibly turned off by a command from the main system device.
The output of the AND circuit 6 is supplied to one input of an OR circuit 7, and the other input of the OR circuit is supplied with an external clock signal. The output of OR circuit 7 is used to update the address counter. To clear the contents of address counter 1, an external clear signal is applied to the clear terminal of the address counter. These external clock signals and external clear signals are controlled by the main body system.
Although not shown, an external clock signal can also be provided to the raster counter.

Data is written into the dot pattern memory 5 as follows. First, AND gate 6 is closed to prohibit updating of address counter 1 by the clock in the display device. Then, the digit counter and the row counter constituting the address counter 1 are connected in cascade, so that the content of the row counter is incremented by 1 by carrying the digit counter. The column counter and row counter are then cleared by sending an external clear signal. After clearing the digit counter and line counter, the external data, ie, the character code, is sent to the display character code memory 3 and written to the address specified by the digit counter and line counter. When this write process is completed, send an external clock signal to increment the contents of the digit counter.
Do 1. After the character code is written to all addresses in the display character code memory 3, the contents of the digit counter and line counter are cleared by an external clear signal, and the digit counter is updated by the carry of the raster counter. do it like this. Then, the character code is read from the display character code memory 3, and the external dot pattern data corresponding to this character code is sent to the dot pattern memory 5, and the read character code and the contents of the raster counter are combined. Write external dot pattern data to the address obtained by combining. After this process is completed, the contents of the raster counter are incremented by 1 using an external clock, and the same process is repeated.

As is clear from the above description, according to the present invention, in a display device in which the dot pattern memory is configured with RAM, data can be written to the dot pattern memory without using a multiplexer or a latch. The circuit configuration of the device can be simplified.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a part of a conventional display device, Fig. 2 is a diagram showing a part of a conventional display device;
The figure is a block diagram of one embodiment of the invention. 1... Address counter, 2... Display character code memory, 3... Latch, 4... Multiplexer, 5... Dot pattern memory, 6...
AND circuit, 7...OR circuit.

Claims (1)

[Claims] 1 comprises a display character code memory in which character codes are stored, an address counter that specifies the address of the display character code memory, and a dot pattern memory consisting of a random access memory, The dot pattern is transferred from the address of the dot pattern memory specified by the character code read from the code memory.
In a display device from which data is read, when writing dot pattern data to the dot pattern memory, the address counter is updated by an external clock signal outside the display device and the display character code memory is updated. Write the character code to
Next, the address counter is cleared with an external clear signal, and then the character code is read from the display character code memory while updating the address counter with an external clock signal, and the dot specified by the read character code is read out. pattern·
A dot pattern device characterized by writing external dot pattern data to a memory address.
Method of writing data to memory.