JPH01118192A - One-chip microcomputer - Google Patents

Abstract

PURPOSE: To eliminate a need of adjustment after assembling by comparing the frequency of a picture display clock with that of a system clock to perfrom adjustment by a program. CONSTITUTION: The output obtained by dividing the frequency of the clock outputted from an oscillation circuit for picture display control by a frequency division ratio set by the program of a microcomputer 8 and the output obtained by dividing the frequency of the system clock of the microcomputer 8 by a prescribed frequency division ratio are compared with each other by a phase comparator 7. Several oscillation resistances incorporated in the oscillation circuit for picture display control are switched by the comparison result to automatically determine the oscillation frequency of a display part, thereby controlling the oscillation frequency for display to a specific value. Thus, the frequency to a desired display position is automatically set by the private circuit and software of the microcomputer to eliminate the need of adjustment after assembling.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a one-chip microcomputer that has a built-in screen display control function for a cathode ray tube, etc., and particularly relates to a display oscillation frequency control device that controls oscillation of a display section. be.

[Conventional technology]

Generally, a one-chip microcomputer with a built-in screen display function is divided into a clock generator 1 in the microcomputer section and a clock generator 2 in the screen display section, as shown in FIG.

The clock oscillation of the microcomputer section often has a function such as a timer or an event counter, so a stable frequency oscillation of a crystal or ceramic resonator is used. On the other hand, the oscillation of the screen display function requires oscillation at different frequencies even with the same circuit configuration depending on the application, so RC integral type oscillation with a simple configuration is often used. In this way, they operate on different clocks even though they are on the same chip.

Now, let's talk about the oscillation of the screen display function in Figures 4 and 5.
This will be explained in detail based on the figures. In order to synchronize with the horizontal scanning line of the screen display, the screen display function stops and starts oscillation in accordance with the synchronization signal. The oscillation circuit of this is a ring oscillation circuit having Schmitt characteristics as shown in FIG.

The oscillation waveform at point A in steady state is the two dark values of Schmitt input. 1, ■, and □, the result will be as shown in Figure 5.

At the rising edge of point B, B=t, ~t2), and at the falling edge of point 0 (1-12~t3), 1=1. at ■i-V LTL % t = L z at V
If i=V, Hl, t.

From equations 3 and 4, and from equations (81 and (9)), the oscillation frequency T becomes 'r=(tz tt )+(tz - tt ) from t2 to t3.

In other words, the oscillation frequency of this oscillation circuit is determined by the input slit width of the Schmitt circuit and the time constant of the external RFC+CFe.

(Problems to be solved by the invention) In a conventional one-chip microcomputer with a built-in screen display function, the display oscillator is an RC integral type, so it takes CF to set the frequency for the desired display position.
Due to variations in C and RFC, it was necessary to use RFC as a semi-fixed variable resistor and make adjustments one by one during the assembly process to assemble the product.

This invention was made to solve the above-mentioned problems, and uses a dedicated circuit and microcomputer software to provide a screen display control function that can automatically set the frequency for the desired display position. The aim is to obtain a one-chip microcomputer with a built-in.

[Means for solving problems]

The one-chip microcomputer according to the present invention divides the clock output from the screen display control oscillator circuit at a division ratio set by the microcomputer program and the system clock of the microcomputer at a predetermined frequency. A phase comparator compares the output obtained by dividing the frequency with the frequency division ratio, and depending on the comparison result of the phase comparator, the display section oscillates by switching several RFCs built in the screen display control oscillation circuit. This allows the frequency to be determined automatically.

[Effect]

In this invention, the clock output from the screen display control oscillator circuit is divided by a frequency division ratio set by a program of a microcomputer, and the system clock of the microcomputer is divided by a predetermined frequency division ratio. The oscillation frequency of the display section is automatically changed by comparing the output obtained from the oscillation with a phase comparator, and switching several R circuits built into the screen display control oscillation circuit based on the comparison result of the phase comparator. Since the configuration is such that the display oscillation frequency can be controlled to a specific value.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, 1 is an oscillation circuit for generating a system clock for a microcomputer, and 3 is a frequency divider for that clock. Further, 2 is a clock generation circuit of the display control section.

6 is a programmable frequency divider whose frequency division ratio can be changed by a microcomputer, which divides the clock of the display control unit; 7 is a system clock frequency division signal and a display clock frequency divided by the programmable frequency divider 6; This is a phase comparator that compares the phase of words. It is assumed that the output of the phase comparator 7 can be read by a microcomputer.

FIG. 2 is a circuit diagram showing details of the display control section clock generation circuit 2, and in the figure, a signal line 4 is a select signal for a resistor group 5 connected in series with RFC.

Next, the operation will be explained.

For example, if the oscillation frequency of the system clock is 4MHz, the frequency is divided by 1/16 by the frequency divider 3, and the oscillation frequency of the system clock is 4MHz.
Assume that 0KHz is input. It is assumed that R3I of the resistor group 5 is selected by the select signal 4 according to the microcomputer program, and the oscillation frequency of the display control clock 2 is set to approximately 5 MHz due to the combination of this and RFe+CFC, and Assuming that the frequency division ratio of the programmable frequency divider 6 is set to 1/20 by the microcomputer program, the output from the programmable frequency divider 6 will be approximately 250 KHz, which is approximately equivalent to the frequency division signal of the system clock °. becomes the frequency. Here, the capacity C a. and resistance RFC is 10-20%
It is thought that there is a certain degree of error, so the actual value is 250KH.
It will be larger or smaller than z.

The phase comparator 7 compares the output from the programmable frequency divider 6 and the divided signal of the system clock, and the CPU 8 of the microcomputer detects this phase difference according to a program, so that the higher the frequency, the lower the frequency. , the register of register group 5 is set to R31 so that the lower the higher the higher the register is.
By reselecting another value from , the oscillation frequency of the display control clock 2 can be corrected based on the system clock. Here, it is assumed that the number of R8, . is arbitrary, and that the degree of change in frequency determined by Rs n + Ry c is several percent.

〔Effect of the invention〕

As described above, according to the present invention, in a one-chip microcomputer with a built-in screen display control function, the screen display clock frequency is compared with the system clock and adjusted by a program. This eliminates the need for adjustment, resulting in cost benefits at the stage of IC usage. It also has the effect of automatically responding to voltage fluctuations and the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a display oscillation frequency control device for a one-chip microcomputer according to an embodiment of the present invention, and FIG. 2 is a diagram showing the internal configuration of a display clock generator used in the embodiment of FIG. Figure 3 is a diagram showing the oscillation circuit of a microcomputer with a built-in screen display control function, Figure 4 is a diagram showing a basic display clock oscillation circuit, and Figure 5 is a diagram showing a basic display clock oscillation circuit.
This figure and FIG. 6 are diagrams showing oscillation waveforms of the oscillation circuit of FIG. 4. 1 is a system clock generator, 2 is a display control clock generator, 3 is a frequency divider, 4 is a select signal, 5 is a group of resistors,
6 is a programmable frequency divider, 7 is a phase comparator, 8 is a CP
U. Note that the same reference numerals in the figures indicate the same or equivalent parts. Figure 1: 4°! Figure 3

Claims (2)

[Claims] (1) In a one-chip microcomputer that has a built-in screen display control function for a cathode ray tube, etc., the microcomputer uses a dividing means to divide the system clock of the microcomputer and a screen display control clock output from a screen display control oscillator. a programmable frequency divider that divides the frequency by a programmed value; a phase comparator that compares the phase of the clock divided by the frequency divider with the phase of the clock divided by the programmable frequency divider; A one-chip microcomputer comprising: frequency control means for changing the frequency of the screen display control clock by switching the oscillation resistor R_F_C of the screen display control oscillator based on the output of the phase comparator. (2) The frequency control means includes a CPU that receives the output of the phase comparator and outputs a selection signal according to a program, and a group of resistors that are provided inside the screen display control oscillator and are switched by the selection signal. The one-chip microcomputer according to claim 1, characterized in that the one-chip microcomputer is comprised of a resistor R_F_C.