JPS6296990A - Cursor display control circuit - 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 Field of the Invention The present invention relates to a cursor display control circuit for controlling data transfer for a cursor sketch on a B7 map display.

BACKGROUND OF THE INVENTION Conventional cursor display processing for bitmap displays includes, for example, the Journal of the Information Processing Society of Japan (Vol.

25.1984. N12. As shown on page 118), the following operations are basically performed.

■ Returning the saved cursor sketch ■ Saving the cursor drawing in a new location ■ Drawing the cursor in a new location In particular, in order to clarify the cursor position, we need to explain the display data of the cursor location. The mask operation as shown in Figure 2 is performed in the above (■). FIG. 2a shows a case where the mask data is subjected to the MND operation and the cursor data is subjected to the FOR operation, and the same figure shows a case where the mask data is subjected to the OR operation and the cursor data is subjected to the ICOR operation.

Next, the procedure for cursor display processing on the video memory will be explained.

■Transfer the saved data to the old display area.

■Transfer the cursor display new area data to the save area.

■ Perform raster operation control and transfer the mask data to the new cursor display area.

■Transfer the cursor data to the new cursor display area by performing a raster operation.

Problems to be Solved by the Invention However, in the above-described processing, the cursor may flicker during display or movement due to the relationship between the rewriting operation of the video memory during data transfer and the timing of the two-star scan.

The flicker phenomenon will be explained using FIG. The horizontal axis in Figure 3 shows time, the vertical axis shows the scan position of raster scan,
The thick solid line shows the relationship between time and raster scan position.

At time to, the vertical blanking interval ends, and scanning of the first line begins. The last line of the display section is scanned at time t1, and the period up to time t2 becomes a vertical retrace section.

Here, consider a case where a cursor with a mask is displayed in the section corresponding to the 41st line to the 422nd line. As shown above, when displaying the cursor, data is transferred to the video memory twice. However, when the relationship between raster scan and data transfer as shown in FIG. 3 arises, data transfer overtakes raster scan.

As a result, an intermediate state of data transfer processing may be displayed on the display screen.

For this reason, there was a problem in that the cursor was displayed in a flickering manner.

In view of this, an object of the present invention is to provide a control circuit that transfers data to a cursor display area without flickering.

Means for Solving the Problems The present invention provides a vertical counter used for generating a CRT synchronization signal, a register for storing the start line and end line of the cursor display position, and respective values of the counter and the register. This cursor display control device includes a comparator that compares the cursor data, a data transfer mechanism that transfers cursor data, and a control circuit that allows data transfer.

According to the above-described structure, the present invention compares the vertical counter and the cursor display position end line at the beginning of transferring mask data for cursor display, and if the counter value is small, causes the data transfer mechanism to transfer the data. forgive. In transferring cursor data, the vertical direction counter and the cursor display position start line are compared, and if the color value is large, the data transfer mechanism is allowed to transfer the data. Data transfer is also allowed during the flyback section. By controlling the data transfer mechanism in this way, the flickering of the υ cursor can be eliminated.

Embodiment FIG. 1 shows a block diagram of a cursor display control circuit in an embodiment of the present invention.

In FIG. 1, 1 is a video memory that stores display data, cursor data, and mask data; 2 is a data transfer mechanism that transfers data in a rectangular area to change display content when data transfer is possible for data in the video memory 1;
3 is a CRT that displays display data read from the video memory 1 in synchronization with a synchronization signal; 4 is a vertical counter used to generate a vertical synchronization signal; 5 is a register that stores the start line of the cursor display position; 6 is a register that stores the end line of the cursor display position, 7 is a comparator that compares the contents of vertical counter 4 and register 6, and outputs "high" if the former is larger than the latter; 8 is vertical counter 4
and a comparator that compares the contents of register 6 with the contents of register 6 and outputs "high" if the former is smaller than the latter; 9 is a selection circuit that first outputs the result of comparator 8 and then outputs the result of comparator 7; 1
0 is a cursor operation request signal, 11 is a vertical synchronization signal, 12
13 is a vertical synchronizing signal indicating a display section, and 13 is a signal indicating a retrace section.

The operation of the cursor display control circuit of this embodiment configured as described above will be described below.

First, a cursor operation request signal 1o is issued, and the cursor display position is written into registers 5 and 6. Next, the values of the vertical counter 4 and the registers 6 and 6 are compared using the comparators 7 and 8, and the results of the comparators 7 and 8 are input to the selection circuit 9. When the cursor operation request signal 1o is first issued, it is latched into the D latch by the vertical synchronization signal 11, and the selection circuit 9 waits until the next vertical synchronization signal 11 arrives.
outputs the result of comparator 8. Next, when the vertical synchronizing signal 11 comes, the selection circuit 9 outputs the result of the comparator.

The output of the selection circuit 9 is used as a permission signal for data transfer for displaying a cursor during the flyback period or the display period, thereby permitting data transfer by the data transfer mechanism.

As described in detail, according to the present invention, data transfer for cursor display can be performed without overtaking the rask scan, and the cursor display does not flicker, and its practical effects are as follows. big.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a cursor display control circuit according to an embodiment of the present invention, Fig. 2 is a pattern diagram showing an example of data processing for cursor display, and Fig. 3 is an example of conventional data transfer and rask scan. FIG. 1...Video memory, 2...Data transfer mechanism, 3...CRT14...Vertical direction counter, 5...Register for storing the song cursor display start line , e...Register for storing the cursor display end line, 7゜8...Comparator, 9...
... Selection circuit, 10 ... Cursor operation request signal, 11 ... Vertical synchronization signal, 12 ... Display section signal, 13 ... Return line section signal . Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (^) (b)

Claims (1)

[Claims] A video memory that stores display data to be displayed on a bitmap display, cursor data, and mask data for performing mask operations on the original image on which the cursor is displayed, and a data transfer mechanism that performs rectangular area transfer of data on the video memory. a CRT for displaying display data read from the video memory; a vertical counter for generating a vertical synchronization signal for the CRT; a register for storing start and end lines of a cursor display position; A first comparator that compares the register storing the cursor end line and detects when the vertical counter is small, and a first comparator that compares the vertical counter and the register storing the cursor start line and detects when the vertical counter is large. and a selection circuit that first outputs the result of the first comparator and then outputs the result of the second comparator, and the selection circuit outputs the result of the first comparator and then the second comparator. The cursor display control circuit is characterized in that it allows the data transfer mechanism to transfer data based on the output of the selection circuit.