JPS6095587A - Display control system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a character display device, and more particularly, to a display control method used in a rask scanning type character display device equipped with a refresh memory.

(b) Background of the Technology In a rask scanning force type character display device, one display surface is divided into equal intervals both vertically and horizontally, and one character is displayed in each cell thus formed. A storage device called a refresh memory is provided to store the code of the character to be displayed in each cell.

The display information to be displayed on the display screen is processed by a microprocessor (M
The character code written in the refresh memory is read in synchronization with the rask scanning signal and converted into dot-shaped pattern data by a 5 character generator.
It is displayed as a dot-like pattern on the display screen.

In such a character display device, the display contents may be changed during display, so when the display control unit that attempts to refresh the display screen and the MPU that attempts to update the display information simultaneously access the refresh memory. There is a problem called memory contention that occurs in

For this reason, character display devices use three types of display control methods, which are broadly classified as sparelet memories.

(C) Prior Art and Problems In the video RAM system, the refresh memory is shared by the display control unit and the MPU, so refreshing is interrupted while the MPU accesses the refresh memory, and at this time a striped pattern appears on the display screen. The disadvantage is that it appears.

In the DMA method, the refresh memory is provided in the memory space of the MPU and is therefore inexpensive. However, when the display control unit attempts to access the refresh memory, M l)
U was forcibly interrupted.

Therefore, if the display screen is refreshed frequently, there is a drawback that the processing speed of the system decreases.

The transparent method was developed to eliminate the above-mentioned drawbacks, and by using a one-time division method, one display control unit and the MPU can access the refresh memory at the same time without conflict. be. However, in this method, 5 display control section and MPt
For example, J is the fresh memory cycle tie J2.
Make it equivalent to 9 because it is accessed alternately every time)' The access time will be halved, so what can be done to prevent this?
The disadvantage is that it is necessary to use a high-speed method with two cans of access time, and the cost of the device increases.

(d) OBJECTS OF THE INVENTION It is an object of the present invention to use slower memory elements and to make them cheaper.

The invention is famous for providing a display control device in which a display control unit and an MPU can simultaneously access the refresh menu without conflict.

(e) Structure of the invention, that is, two display control systems according to the present invention: (1) a refresh memory that stores character information to be displayed on the display surface using a character code in correspondence with the position of the display surface -L; and an address line of the refresh memory. and a two-person address multiplexer that accesses in a time-sharing manner, the display control device performs refreshing of the display surface and updating of the storage contents of the refresh memory in a time-sharing manner.

The time allocated for the refresh is longer than the time allocated for updating the refresh memory.

(f) Examples of the Invention The gist of the present invention will be specifically explained below using examples.

FIG. 1 shows a block diagram of a display control circuit according to the present invention. In the figure, 1 indicates all synchronization signals or timings necessary for displaying the contents of a refresh memory 4 (described later) on a display screen (not shown). 2 is a microprocessor (MPU) used to update the storage contents of refresh memory 4 via a keyboard (not shown); 3 is for accessing address lines of refresh memory 4, which will be described later. A two-man-operated address multiplexer, 4 is a fresh memory that stores character information to be displayed on the display screen in correspondence with the position on the display surface using a character code, and 5 is a refresh memory 4.
6 is a character generator that generates a character pattern corresponding to the character code given from the refresh memory via the data latch 5; 7 is a character generator that is obtained from the character generator 6; This is a shift register that inputs character patterns in parallel and outputs them in series.

Needless to say, access to the refresh memory 4 is performed in cycle time units, and α is the cycle time of the refresh memory 4, n is the number of cycle times allocated to the refresh L.Sosh, and is the number of cycle times allocated to updating the refresh memory 4. Let m be the time required to display a pattern for one scan in one character (character time) as β.

(n+m)α=nβ That is, β-(1+m/, n)α Here, since n>m, α>β/2 On the other hand, conventionally, since n=m, α1-β/2 and α >α1 In other words, to obtain the same character time β, a memory element with a longer cycle time than the conventional one can be used.

In addition, in Fig. 2, α-200ns ・β-300ns −
This is an example of a time chart of signals in each part of the display control device when n/m=2/I, (a) access to the refresh memory 4, (b) reading data from the refresh memory 4, (C) ) is the output of the first stage of the data latch 5, (d) is the output of the second stage of the data latch 5, (e) is the output of the character generator 6, and (f) is the output of the shift register 7.

(g) Detailed Description of the Invention As described above, according to the present invention, it is possible to obtain a display control device that is cheaper than the conventional transparent method.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a display control device according to an embodiment of the present invention, and FIG. 2 is an example of a signal time chart regarding the embodiment. In the figure, 1 is a synchronization signal generation circuit, 2 is a microprocessor, 4 is a refresh memory, and 6 is a character generator. 9) Tomoe b

Claims (1)

[Claims] The display screen includes a refresh memory that stores character information to be displayed on the display screen in accordance with a character code corresponding to a position on the display screen, and a two-man address multiplexer that accesses the address lines of the refresh memory in a time-sharing manner. A display control method in which a display control device performs refreshing and refreshing/updating the memory contents of the refresh memory by time allocation, characterized in that the time allocated to the refreshing is longer than the time allocated to updating the refresh memory.