JPS6112274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization method for horizontally synchronizing each raster when a character screen and a graphic screen are displayed in a superimposed manner by raster scanning.

Conventionally, when displaying a character screen consisting of a code buffer and a graphic screen consisting of a bit pattern memory on a cathode ray tube (CRT) using raster scanning, the sampling clock for video generation on both screens must be the same or horizontally Although the running time is an integral multiple of the least common multiple of both clock periods,
If the number of characters on the text screen is large, or the number of displayed dots on the graphics screen is large, there may be restrictions on the character font, number of characters, frame frequency, etc.
There is a drawback that screen flickering becomes noticeable due to a decrease in frame frequency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a synchronization method that reduces character restrictions and screen flicker when displaying a character screen and a graphic screen in a superimposed manner using raster scanning.

In order to achieve the above object, the method of superimposing and synchronizing character and graphic screens of the present invention overlaps the character screen and the graphic screen, which are respectively composed of video signals from the character pattern and graphic bit pattern generating means, on the display screen by raster scanning. In a display device, if the periods of the video generation sampling clocks for the character screen and the graphics screen are different and the horizontal scanning period is not a common multiple of the two clock periods, This method is characterized by interrupting and correcting the sampling clock of the screen during the blanking period so as to synchronize the start point of video generation with the synchronization point of raster scanning.

The present invention will now be described in detail with reference to examples.

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention.

In the figure, a control signal from an external control circuit is input to a CRT control circuit 3 and a graphic control circuit 7 via a control circuit 1, a character code is read from a character screen buffer 2, and a character pattern is generated by a character generator 5. A character video signal generator (VSG) 6 performs parallel-to-serial conversion, and the video signal is sent to a CRT 11 via an OR circuit 10. At the same time, CRT control circuit 3
From horizontal sync signal (HS), vertical sync signal (VS)
is input directly to the CRT11 for synchronous control. In addition, the graphic bit pattern is read from the graphic screen buffer 8, and the graphic video signal generator (VSG) 9 performs parallel-to-serial conversion to convert the video signal into the same format as characters.
It is sent to the CRT 11 via the OR circuit 10. Also CRT
The horizontal synchronization signal (HS) is input from the control circuit 3 to the oscillation circuit 4, and the synchronization signal (SYNC) is output, and the character screen clock (CCLK) 1 to m and the graphic screen clock (GCLK) 1 to n are synchronized for the raster. will be carried out. CCLK1~m are given to VSG6,
CCLK1-n are applied to VSG9 and used as sampling clocks for generating video signals.
Figure 2 a shows the sampling clock for the character screen, and synchronization b shows the sampling clock for the graphic screen.
It works. In this case, in the present invention, the sampling clock of one screen is forcibly interrupted by the SYNC signal during the blanking period so that a synchronization point is determined for each raster and synchronization is always performed at that point.

FIGS. 3a to 3e are explanatory diagrams of a method for synchronizing character and graphic screens according to the present invention.

It is assumed that the HS in a of the figure is synchronized with CCLK1 to CCLK of b in the figure. In the present invention, GCLK1 to GCLK1 to c in the same figure
In order to forcibly synchronize CCLK1 to CCLK1 to m in figure b during the blanking period of HS in figure a,
Using the SYNC signal of GCLK1~n in the same figure c,
The operation is interrupted at the same time point A of the HS raster so that it is an integer multiple of the least common multiple of m and n. In other words, the SYNC signal in figure d enters the blanking period, GCLK is turned on at m counts, and at this time
GCLK maintains count m. Then, the SYNC signal is turned off before the synchronization point A is an integral multiple of the greatest common multiple of m and n. As shown in the video signal in figure e,
It starts at the synchronization point A and ends at the last synchronization point B of the rask interval. What should be noted here is that the integer multiple of the least common multiple of m and n is required for the period from the time when the SYNC signal is turned off to the synchronization point A, and not for the horizontal scanning period. Therefore, the first screen, CCLK1 to CCLKm here, is synchronized with the horizontal synchronization signal HS, and the second screen is temporarily interrupted during the blanking period and is always synchronized with the beginning of the raster by the synchronization clock. It is configured to synchronize at synchronization point A.

Also, in Fig. 3, the synchronization point A of CCLK1~m and GCLK1~n is specified at count 1, but
The selection of this count is not limited to this point.
In other words, the display positions of the character screen and the graphic screen can be set in dot units.

As explained above, according to the present invention, when a character screen and a graphic screen are displayed in a superimposed manner by raster scanning, horizontal synchronization is achieved by interrupting the sampling clock of one screen at the synchronization point for each raster. By doing so, it is possible to realize a synchronization method with fewer character restrictions and fewer screen flickers.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention,
Figures 2a and b are diagrams explaining the principle of the present invention, Figures 3a to 3
e is an explanatory diagram of the operation of the main parts of the present invention, in which 1 is a control circuit, 2 is a character screen buffer, 3 is a CRT control circuit, 4 is an oscillation circuit, 5 is a character generator, 6, 9
1 is a video signal generator, 7 is a graphic control circuit, 8 is a graphic screen buffer, 10 is an OR circuit, and 11 is a CRT.

Claims (1)

[Claims] 1. In a device that displays a character screen and a graphic screen overlappingly on a display screen by raster scanning, each consisting of a video signal from a character pattern and a graphic bit pattern generating means, the sampling clock for video generation of the character screen and the graphic screen is The period is different,
If the horizontal scanning time is not a common multiple of both clock cycles, the blanking period is set so that the video generation start point of the screen whose horizontal scanning time is not a common multiple of the sampling clock cycle is synchronized with the synchronization point of raster running. A weight synchronization method for character and graphic screens characterized by interrupting and correcting the sampling clock of the screen.