JPH02210494A - Color look up table circuit - Google Patents

Abstract

PURPOSE:To allow multicolor simultaneous displaying without deteriorating the characteristics of an analog signal and without complicating circuits by providing a switching circuit which leads out the output of a color data storage memory (SRAM) and external input data selectively to a digital to analog (D-A) converter. CONSTITUTION:The switching circuit 13 for switching to the input from an external circuit is connected between the SRAM 12 and the D-A converter 15 of the color look up table circuit to allow the multicolor simultaneous displaying by the color data form the external circuit. Namely, color data is switched while the data is the digital signal and, therefore, no influence is exerted to the characteristics of the analog signal after the conversion by the D-A converter 15. The external circuit functions merely to generate the control signal 8 for switching the color data and the data from the outside. The degree of freedom for the external circuit and diffusivity are improved in this way.

Description

TECHNICAL FIELD The present invention relates to a color look-up table circuit, and more particularly to a color look-up table circuit having a color data storage memory for storing color data.

Prior Art This type of color look-up table circuit converts color data displayed on a display screen into an analog signal and sends it to a display, and is already known. Second
The figure is a block diagram showing an example of such a color lookup table circuit.

An SRAM (static random access memory) 11 that stores color data to be displayed on the screen, and this SRAM
a read/write control circuit 2 that controls color data input/output, address output, etc. during MII read/write;
An address control circuit that converts the display data from the display data bus 6 into an SRAM II address and switches it to the SRAM II address for reading and writing.
A DA (digital analog) converter 15 converts the output of M1l into an analog signal 16.

The color data stored in SRAMII is read by controlling the read data bus 3, write data bus 4, and read/write address bus 5 by the read/write control circuit 2. That is, at the time of writing, the color data input from the read/write control circuit 2 to the SRAM 11 via the write data bus 4 is written to the position specified by the address. When reading, SRAMII
This is done by reading the color data stored in the address from the position specified by the address and inputting it to the read/write control circuit 2 via the read data bus 3.

In addition, the address control during read/write is
The address, which is common both during writing and is output from the read/write control circuit 2 to the read/write address bus 5, enters the address control circuit 9 which is switched to the input from the read/write address bus 5 only during read/write. This is done by inputting the data to SRAM II via the SRAMII.

The screen is displayed as follows. Display data input from the display data bus 6 enters the address control circuit 9, is converted into an address, and is sent to the SR via the address bus 10.
Enter AMII. The color data is read from the position specified by this address and sent to D- through the SRAM output bus 12.
is input to the A converter 15, and this D-A converter 1
5 into an analog signal 16.

In such a color lookup table circuit, S
By using a RAM and reading out n-bit color data for an m-bit address, multicolor display is possible. Normally, the number n of color data bits is larger than the number m of address bits. For example, if there is 12-bit color data for a 4-bit address, 16 out of 4096 colors can be displayed.

Furthermore, the color look-up table circuit is often constructed of a single LSI chip in order to increase speed and reduce power consumption due to higher display resolution.

The conventional color look-up table circuit described above uses an SRAM with m address bits and n data bits to enable multicolor display, but the number of colors that can be displayed simultaneously is limited to 2m colors.

Also, by increasing the number of bits m of the SRAM address,
Increasing the number of colors that can be displayed at the same time is difficult to achieve because it increases the size of the circuit that inputs display data into the color lookup table circuit and the memory that stores the display data. Therefore, usually
By adding another circuit later, multiple colors can be displayed as needed.

However, in the conventional circuit, since the circuit is composed of a single LSI chip, the analog signal output from the LSI must be switched, which has the disadvantage that the characteristics of the analog signal deteriorate.

Furthermore, it is necessary to provide a separate analog circuit in the external circuit, which also has the disadvantage of complicating the circuit.

OBJECTS OF THE INVENTION An object of the present invention is to provide a color look-up table circuit that can display multiple colors simultaneously without any restrictions without deteriorating the characteristics of analog signals or complicating the circuit.

According to the present invention, there is a color data storage memory in which color data is stored in advance and indexed by display data from a host device, and the color data that is the index result from the color data storage memory is converted into an analog signal. A color look-up table circuit includes a digital-to-analog converter for converting the analog signal and sends the analog signal to a color display section, the circuit selectively converting the output of the color data storage memory and external input data into the digital signal. and a switching circuit leading to an analog converter.

X ships a week Next, the present invention will be explained with reference to the drawings.

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

Consists of data bus 1, read/write control circuit 2, read data bus 3, write data bus 4, read/write address bus 5, display data bus 6, address control circuit 9, address bus 10, SRAM II, and SRAM output bus 12. , the circuit before the switching circuit 13 operates in the same way as the example of the conventional color look-up table circuit shown in FIG.

The switching circuit 13 switches between the color data input from the external direct input bus and the color data input from the SRAM output bus, and outputs the data to the DA converter input bus 14.

The control signal 8 is a switching signal for switching the switching circuit 13 from outside.

The D-A converter 15 is connected to the D-A converter input bus 14
color data is converted into an analog signal 16.

For example, the display data bus 6 handles 4-bit data,
If the input of the I)-A converter 15 handles 12-bit data, the SRAM II will output 12-bit color data for a 4-bit address, and the switching circuit 13 will output 12-bit color data from the SRAM output bus 12. When switching to the input mode, 16 out of 4096 colors can be displayed simultaneously.

Here, a circuit for generating 12-bit color data is added externally, the 12-bit color data is input from the external direct input bus flow, and the switching circuit 13 is switched to the input of the external direct input bus flow by the control signal 8. By converting the 12 bits of color data directly input to the D-A converter into an analog signal, it is possible to display 4096 colors simultaneously.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-mentioned embodiments. Then, when displaying with color data from SRAM II, 2 of 2" colors will be displayed simultaneously, and when displaying with externally input color data, 2' of 2" colors will be displayed simultaneously.
Colors will be displayed simultaneously.

As explained above, according to the present invention, a switching circuit for switching input from an external circuit is connected between the SRAM and the DA converter of a conventional color lookup table circuit, and the input from the external circuit is connected. Since the color data is switched into the digital signal, it has the advantage that it does not affect the characteristics of the analog signal after being converted by the D-A converter.

Also, as an external circuit, it only generates a control signal for switching between color data and external data.
This has the effect of increasing the degree of freedom with respect to external circuits and increasing expandability. Furthermore, since a switching circuit is added to the conventional circuit to increase external expandability,
It has the effect of being able to fully respond to miniaturization and high integration due to LSI.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional color look-up table circuit. Explanation of symbols of main parts 9...Address control circuit 11...S RAM 13...Switching circuit 15...D-A converter

Claims (1)

[Claims] (1) Includes a color data storage memory in which color data is stored in advance and indexed by display data from a host device, and a digital-to-analog converter that converts the color data that is the index result from the color data storage memory into an analog signal. , a color look-up table circuit configured to send this analog signal to a color display section, and a switching circuit configured to selectively output the output of the color data storage memory and external input data to the digital-to-analog converter; A color lookup table circuit comprising: