JPH0452882A - Microcomputer mounting picture display function - Google Patents

Abstract

PURPOSE:To obtain using methods corresponding to various system designs by preparing a clock to be used only for a picture display device in addition to a CPU clock, selecting the display device clock to use it for generating an operation clock pulse for the display device. CONSTITUTION:A signal '1' or '0' is outputted from a register 7 based upon an instruction outputted from a CPU 1 and either one of the CPU clock 4 and a picture displaying oscillator 5 is inputted to the picture display device by a clock pulse selecting circuit 8 as a clock pulse source. Since the clock of the oscillator 5 can be used for the operation clock pulse source. Since the clock of the oscillator 5 can be used for the operation clock pulse of the device 2 without being restricted by the frequency of the CPU clock 4, the operation frequency can easily be changed. Since the device can also be driven even when the CPU clock 4 is selected as the operation clock pulse source of the device 2, it is unnecessary to externally connecting the oscillator 5, the number of connection pins can be reduced and the microcomputer can be used correspondingly to various systems.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides clock pulses for screen display devices.
The present invention relates to a single-chip microcomputer that can be switched to operate either using a central processing unit f (hereinafter referred to as CPU) clock or using screen display oscillation.

[Conventional technology]

FIG. 5 is a part of a system block diagram of a conventional microcomputer. In the figure, fil is the CPU inside the semiconductor circuit, (2) is the screen display device, and (3) is the CPU.
A screen display clock control circuit that generates screen display clock pulses from the U clock, and (4) a CPU clock (Ceralock oscillator) for operating the CPU. (4), CPU il+ and screen display device (2)
Both circuits are operating.

[Problem to be solved by the invention]

Microcomputer with built-in conventional screen display device
is CPU (11, screen display bag W (2) are both CPU
Although it is operated using a clock (4) (Ceralock oscillator), in this case, the operating frequency of the screen display device (2) is limited by the frequency of its CPU clock (4).

When displaying characters, etc. on the screen of a TV or the like, it becomes difficult to adjust the display position in the horizontal direction depending on the operating frequency of the screen display device. In addition, when you want to display characters using the high scan function used in high-definition TVs, the horizontal synchronization signal interval is 63.5 μsec for conventional TVs, but in high scan, scanning is performed at 31.25 μsec. To make it compatible, it is necessary to double the operating frequency, and by doing so, the screen display function can be used as before, but if the operating frequency cannot be changed, it can be displayed on a conventional TV screen. This means that only half of the number of characters can be displayed. This invention was made to solve this problem, and even if the clock pulse generated from the CPU clock by the screen display clock control circuit is used, the clock pulse from another screen display oscillation is used. Also enable the screen display device, select both,
The purpose is to provide a microcomputer that can be switched.

[Means to solve the problem]

A microcomputer equipped with a screen display function according to the present invention includes a central processing unit inside a semiconductor and a screen display device for displaying characters, numbers, symbols, etc. on a screen such as a TV, and has a clock pulse of the screen display device. The present invention is characterized by a selection means for the oscillation circuit of the screen display device for selecting the source of the clock pulse from the oscillation circuit of the clock of the central processing unit or the clock pulse of the dedicated oscillation circuit of the screen display device. .

[Effect]

According to this invention, in addition to the CPU clock, another clock dedicated to the screen display device is provided, so either the CPU clock or the clock dedicated to the screen display device can be selected and used as the operating clock pulse of the screen display device. I can do it.

〔Example〕

FIG. 1 is a system block diagram showing an embodiment of the present invention. (II, (21, (3), (4) are equivalent to those in the conventional example. In the figure, (5) is for screen display that generates a clock to operate the screen display device (2). oscillation.In such a circuit,
CP tJ (11 operates with the clock pulse of the oscillation circuit of the CPU clock (4), but the screen display device! +21
In this case, the clock pulses of the CP tJ clock (4) oscillation circuit, or the clock pulses of another screen display oscillator (5) externally connected, can be used to operate both. Allows software selection and switching. FIG. 2 is an example of a circuit diagram of the switching portion of the clock pulse. (6) is memory,
(7) is a register, and (8) is a clock pulse selection circuit. A signal of 1 or O is output from the register (7) according to the command from CPTJ, and the clock pulse selection circuit (8) outputs the CPU clock (4) or the screen display oscillation (5) to the screen display device (2). Either one will be input as a clock pulse source. that way,
The clock of the screen display oscillation (5) can be used as the operating clock pulse of the screen display device (2) without being constrained by the frequency of the CPU clock (4), and the operating frequency can be easily changed. can. Also, the screen display device!
(It can also operate even if the CPU clock (4) is selected as the operating clock pulse source of 21, so in that case there is no need to externally connect the screen display oscillator (5) and the number of pins can be reduced. The system designer can select and use either the CPU clock (4) or the screen display oscillation (5) depending on the system in which the microcomputer with the screen display function is installed. This is an embodiment using a CERALOCK oscillator as a specific example of the display oscillation (5). In FIG. There is a slight time lag until the clock is generated, so it is used without stopping oscillation like the normal CPU clock (4).For this reason, the screen display device (2)
When used as an operating clock, the screen display clock control circuit (3) is manually controlled to generate a lock pulse that starts oscillating in accordance with the timing of the horizontal synchronization signal. The screen display device (2) can be operated by selecting the clock input to the control circuit (3) from the CPU clock (4) or the clock from the CERALOCK oscillator (5a). FIG. 4 shows an embodiment using an RC oscillator as a specific example of the screen display oscillation (5) in FIG. In FIG. 4, (5b) is an RC oscillator. In the case of the RC oscillator (5b), a clock can be generated immediately even if a clock signal is started. Therefore, it can be used as an operating clock for the screen display device (2) without inputting it to the screen display clock control circuit (3). However, since the CPU clock (4) is first input to the screen display clock control circuit (3) to generate the operating clock pulse for the screen display device (2), both clock pulses are input to the screen display device (2). It is possible to select it when inputting.

〔Effect of the invention〕

As described above, according to the present invention, since the selection means for using either the CPU clock or the oscillator dedicated to the screen display device as the oscillation for screen display is provided, the west side display device can be operated at a frequency different from the CPU clock. If you want to operate with 7 clock pulses, you can select and switch to a clock pulse from an oscillation circuit dedicated to screen display, which is separate from the CPU clock, which has the effect of enabling usage methods that suit various system designs. .

[Brief explanation of drawings]

FIG. 1 is a system block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing the switching part of the clock pulse source in FIG. 1, and FIGS. 3 and 4 are other embodiments of the present invention. FIG. 5 is a system block diagram of a conventional microcomputer. In the figure, +11 is the CPU, (2) is the screen display device,
(3) is the screen display clock control circuit, (4) is the CPU
Clock (5) (5a) (5b) is a clock pulse dedicated to the screen display device, (6) is a memory, (7) is a register, and (8) is a clock pulse selection circuit. In each figure, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa Figure 1 Figure 3 Figure 2 Figure 4 Figure 5! Translation e-pay 2, name of invention 3. Procedural amendment written by the person making the amendment (voluntary) September 29, 1990 Microcomputer with screen display function Representative Kizunya Mitsubishi Electric Corporation (Contact number 03 (213) 3421 Patent Department) 15, Claims column and Detailed description of the invention column of the specification to be amended. 6. Contents of amendment (1) The scope of claims in the description will be corrected as shown in the attached sheet. (2) On page 3 of the specification, line 3: “31.
254 Sec” to “31.75 in Biscan”
With fisec,” he corrected. (3) It is possible to switch r on page 5, line 5 of the specification. ” should be corrected to “enable switching.” 7゜ List of attached documents (1) One or more documents stating the amended scope of claims; scope of claims;

Claims (1)

[Claims] The semiconductor is equipped with a central processing unit and a screen display device for displaying characters, numbers, symbols, etc. on a screen such as a TV, and the clock pulse source of the screen display device is connected to a clock oscillation circuit of the central processing unit. Clock pulse?
A microcomputer equipped with a screen display function, characterized by selecting means for selecting an oscillation circuit of the screen display device for selecting a clock pulse of a dedicated oscillation circuit of the screen display device.