JPH02133820A - Display control system - Google Patents

Abstract

PURPOSE:To increase the character display speed by adding an additional circuit consisting of a DMA control circuit, a DMA instruction register, and a DMA operation table to an existing system. CONSTITUTION:A DMA control circuit 7 of an additional circuit 10 refers to the data registered in a DMA instruction register 6 and a DMA operation table 9 to decide a DMA address and a memory access mode. Then the circuit 7 outputs a DMA request control signal 11 to a microprocessor 1 and performs a DMA with the permission of the microprocessor 1. A first DMA includes the accesses to a font memory 4 and a video memory 5. Then both accesses are carried out at one time and the pattern data of one byte is transferred. Thus it is possible to increase the character display speed and to decrease the corrections of the existing programs.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a display control method for a display device using a microcomputer, and particularly to a bitmap method in which a display pattern is stored in correspondence with one bit of a video memory. The present invention relates to a display control method in a display device.

[Prior Art and Problems to be Solved by the Invention] Writing a character pattern into a video memory using the bitmap method involves data transfer to a rectangular area due to the nature of the character pattern. Additionally, data write operations often require consideration of bit boundaries.

Therefore, a microprocessor normally performs address calculations and data transfer under program control. Therefore, compared to a character-based video memory, the program IIJII takes more time and the display speed is considerably slower.

In addition, display devices that use LSIs dedicated to display control have the ability to perform high-speed data transfer between video memory and font memory for displaying characters, but there are restrictions on the system configuration of the font memory. I have something to give.

For example, font memory often has to be connected to the same local bus to which video memory is connected with a linear address configuration, so accessing font memory from the system bus requires access to this display control LSI. It is necessary to intervene, and memory control dependent on the LSI is required.

The conventional display #I method will be further explained using the drawings.

FIG. 5 is a system configuration diagram in a conventional display $17 control system. FIG. 6 is a program flowchart for character display in the conventional system shown in FIG.

The pattern data stored in the video memory 5 is read out by the display control circuit 6, and one bit of the data is displayed corresponding to one pixel on the screen.

My processor 1 is executed by the control program stored in ROM 2 according to the flowchart shown in FIG. First, attributes such as the number of bytes in the contraction direction and horizontal direction of the character pattern data to be displayed and the presence or absence of decorative display are created (process 401) Next, the font in which the character pattern data to be displayed is stored A read address for the memory 4 is created (process 402). Next, an address for the video memory 5 to write the read pattern data is created (process 403). Next, 1 byte of pattern data is written from the font memory 4. Read processing 4
04), writes this data to the video memory 5 (process 405), then checks whether all pattern data has been transferred, and if NO, returns to process 402 and returns process 402 to process 405. return (processing 406),
Once the transfer is complete, the process ends.

Normally, the pattern data stored in the font memory 4 is in continuous addresses, so the read address only needs to be incremented by 1 byte, but the write address in the video memory 5 depends on the display screen configuration. Calculations must be made taking into account screen parameters.

[Means for Solving the Problems] An object of the present invention is to provide a display control method that solves the drawbacks of the conventional methods described above, can speed up character display, and requires less modification to existing programs. It is.

The display control method of the present invention that achieves the above object includes a bitmap video memory, a font memory that stores character pattern data to be written to the video memory,
A DMA operation table in which addresses and access modes are registered in the order of memory access, a font memory read address, and a video memory write address, with a series of memory operations for writing one character of pattern data to the video memory as one set. and a DMA instruction register for registering the character pattern type, and a DMA instruction register for registering the contents of the DMA instruction register and the DM
DMA while referring to the contents of the A operation table.
A DMA1llJm circuit that performs data transfer by DMA in the order of the operation table.

[Example] The display control method of the present invention will be described below with reference to the drawings.

FIG. 1 is a system configuration diagram of an embodiment of the display control method according to the present invention.

In FIG. 1, the internal component 10 surrounded by a broken line is a part added to the conventional display control method shown in FIG.

Character display control according to the system configuration of the present invention is executed according to the flowchart shown in FIG.

In FIG. 1, a DMA control circuit 7 refers to a DMA command register 8 and data registered in a DMA operation table 9, determines a DMA address and a memory access mode, and sends a DMA request control signal 11 to a microprocessor 1. is output, and DMA is performed with permission from the microprocessor 1. Furthermore, the DMA control circuit 7 executes DMA in the order of the access sequence numbers registered in the DMA operation table 9 shown in FIG. Both accesses are executed simultaneously to transfer 1 byte of pattern data. As the DMA address, the sum of the base address registered in the DMA instruction register 8 and the offset address registered in the DMA operation table 9 is output.

Font memory side address: (a+X) Video memory straw 1 address: (b1y) Also, DMA
In the operation table 9, DMA access modes for both the font memory side and the video memory side are registered. In the example shown in FIG.
W> is executed.

DMA automatically terminates when the access sequence number or end is reached.

The contents of the DMA operation table shown in FIG.
1) is registered as.

During character display operation, the DMA command register 8 shown in FIG.
Data t1 of the character pattern type is referred to, and data in the DMA operation table having a character pattern type that matches this is selected by the DMA control circuit.

In the flowchart of FIG. 4, first, the pattern type of characters to be displayed is identified and set in the DMA command register 8 (process 501). Next, a read address for the font memory 4 that stores the character pattern is created and set in the DMA command register 8 (process 502).Next, an address for the video memory 5 where the character pattern is written is created and the DMA command register 8 is set.
It is set in the A command register 8 (process 503), thereby executing DMA transfer of pattern data, and if necessary, checking for completion of the transfer (process 504).

As explained above, when the circuit of the present invention is added to a conventional system configuration, the only change to the program is to change the flowchart of FIG. 6 to that of FIG. 4, and other processing is not affected. Furthermore, conventional display control is also possible.

The DMA operation table 9 in FIG. 1 does not need to store table data for all pattern types, and can be stored in the ROM by the system control program when necessary.
2 or may be loaded from the system RAM 3. This makes the DMA operation programmable and can flexibly respond to changes in display specifications. Also,
The access mode of the DMA operation table in FIG. 3 can be set to I10 access, and it is possible to speed up the access to the video memory by setting it to modify write. Furthermore, it is not necessary that the number of accesses on the font memory side and the number of accesses on the video memory side match, and it is also possible to write the same font data to the video memory divided into banks at high speed.

[Effects of the Invention] As explained above, according to the present invention, a. character display can be achieved by adding an additional circuit according to the present invention to an existing system having a bitmap type video memory and a font memory connected to a system bus; This makes it possible to speed up the process.

b1 When the circuit of the present invention is added to an existing system, there is an advantage that less modification is required to the existing program because the influence on the system is small.

There are effects such as

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of an embodiment of the display control method according to the present invention. FIG. 2 is a diagram of a table representing the contents of the CAM instruction register of FIG. 1. FIG. 3 is a diagram of a table representing the contents of the CAM operation table of FIG. 1. FIG. 4 is a program flowchart for character display according to the present invention. FIG. 5 is a system configuration diagram in a conventional display control method. Figure 6 shows one of the character displays in the conventional system shown in Figure 5.
0g flowchart. 1... Microprocessor 2... ROM3.
...System RAM 4...Font memory 5
...Video memory 6...Display control circuit 7.
...DMA control circuit 8...DMA instruction register 9
...DMA operation table 11...DM
A request control signal 12...system bus

Claims (1)

[Scope of Claim] A display device that operates under program control by a microprocessor, comprising: a bitmap video memory; a font memory that stores character pattern data to be written into the video memory; A DMA operation table in which addresses and access modes are registered in the order of memory access as one set of a series of memory operations for writing to the video memory, and the read address of the font memory, the write address of the video memory, and the character pattern type are registered. a DMA instruction register, and a DM that performs data transfer by DMA in the order of the DMA operation table while referring to the contents of the DMA instruction register and the contents of the DMA operation table.
A display control system consisting of a control circuit and.