JPH075855A - Microcomputer with function of on-screen display - Google Patents

Abstract

PURPOSE:To automatically adjust frequency of a display clock for on-screen display. CONSTITUTION:A oscillator clock 17 outputted from a CR oscillator constituted of a resistor array 12 and capacitors 21, 22 is counted by a oscillation pulse counter 18. A synthesized resistance value of the resistor array 12 is decided by combination of connection of each switch of a switch group 13 based on control of a combination circuit 14. The oscillator pulse counter 18 counts the inputted oscillator clock 17, outputs a count 27 at the time of input of a start stop signal 10, and sets it to a control register 28. The combination circuit 14 changes combination of connection of each switch of the switch group 13 based on a counted value set to the control register 28. Thereby, the synthesized resistance value of the resistor array 12 is changed, and outputted oscillation clock frequency is automatically adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer having an on-screen display function.

[0002]

2. Description of the Related Art Recently, television receivers and CRT monitors are equipped with various functions, one of which is a so-called on-screen display function. This function is a function of displaying, for example, characters / symbols or figures for displaying the channel number, the volume, etc. on the screen so as to be superimposed on the image. Such a function is generally realized by a circuit built in a one-chip microcomputer. In this case, the character display is performed based on a dedicated display clock different from the system clock of the microcomputer.

FIG. 5 shows a conventional one-chip microcomputer having an on-screen display function. In addition to a character display control circuit (not shown), the microcomputer 40 is provided with a NAND gate 11 to which a start / stop signal 10 for controlling the start and stop of character display is input. The other input terminal of the NAND gate 11 is the external terminal 4 provided on the chip.
1 and the output side is the external terminal 4 of the chip.
Connected to 2. A CR oscillation circuit including capacitors 43 and 44 and a variable resistor 45 is connected to the external terminals 41 and 42. Then, the resistance value of the variable resistor 45 of this oscillation circuit is manually adjusted to obtain a predetermined oscillation frequency.

FIG. 6 shows an example of another conventional microcomputer with an on-screen display function. In this example, a coil 46 is provided instead of the variable resistor 45.

[0005]

As described above, in the conventional microcomputer with the on-screen function, the clock used for display is generated by the external CR oscillator or LC oscillator. However, there is a problem that the external LC oscillator is relatively expensive, and particularly the unadjusted LC oscillator is more expensive. Further, in the case of the external CR oscillator, there is a problem that the frequency changes largely due to voltage and temperature, and the oscillation frequency must be manually adjusted.
Further, there is a problem that an external terminal for external attachment is additionally required.

Further, in the field of CRT monitors, it was necessary to change the frequency of the oscillator by following changes in the frequency of the horizontal synchronizing signal.

The present invention has been made to solve the above problems, and an object of the invention is to obtain a low-cost microcomputer with an on-screen display function that does not require the trouble of adjustment and has the number of external terminals reduced as much as possible. To do.

[0008]

According to a first aspect of the present invention, there is provided a microcomputer with an on-screen display function, which is a microcomputer having an on-screen display function for displaying character information on a CRT screen so as to be superimposed on an image. There, (i) an oscillator composed of a resistor array consisting of a plurality of resistors and a capacitor, (ii) a switch group for turning on and off the connection of each resistor of the resistor array, (iii) the oscillator (Iv) a counter for counting the oscillation clocks, and (iv) a combination control circuit for controlling the on / off combination of the switches of the switch group in accordance with the count value from the counter.

A microcomputer with an on-screen display function according to a second aspect of the present invention is a microcomputer having an on-screen display function for displaying character information on a CRT screen so as to be superimposed on a video image. An oscillator composed of a capacitor array composed of a plurality of capacitors and a resistor, (ii) a switch group for turning on and off the connection of each capacitor of the capacitor array, and (iii) a counter for counting the oscillation clock of the oscillator. And (iv) a combination control circuit for controlling the on / off combination of each switch of the switch group according to the count value from this counter.

[0010]

In the microcomputer with an on-screen display function according to the first aspect of the present invention, the number of oscillation clocks of the oscillator is counted, and the combination of resistors in the resistor array is changed according to the count value to combine the resistors. The resistance value changes, which changes the oscillation clock frequency of the oscillator.

According to another aspect of the present invention, there is provided an on-screen display function microcomputer, wherein the number of oscillation clocks of an oscillator is counted, and a combination of capacitors in a capacitor array is changed according to the counted value, thereby producing a combined capacitance. Changes, which changes the oscillation clock frequency of the oscillator.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a microcomputer with an on-screen display function according to a first embodiment of the present invention. This circuit is provided with a NAND gate circuit 11, and on the output side thereof, a resistor array 12 connected in series and a capacitor 21 whose one end is grounded,
A CR oscillator composed of 22 is connected. One end of each resistor of the resistor array 12 has a switch group 1
3 are connected to each other via respective switches, connected to a character display control circuit (not shown) via an inverter 15, and connected to an oscillation pulse counter 18. Each switch of the switch group is turned on / off in a predetermined combination under the control of the combination circuit 14.

The oscillation pulse counter 18 counts the oscillation clock 17 from the oscillator, outputs the count value 27 at the time when the start / stop signal 10 corresponding to the right end of the screen is input, and sets it in the control register 28. Has become. The combination circuit 14 performs the above-mentioned combination control based on the value of the control register 28.

The operation of the microcomputer configured as described above will be described with reference to FIG. When the start / stop signal 10 is input to the NAND gate 11 of this circuit in synchronization with the horizontal synchronizing signal (FIG. 2B), the CR oscillating circuit including the resistor array 12 and the capacitors 21 and 22 causes the resistor array 12 to be combined. It oscillates a clock with a frequency corresponding to the resistance value. Here, the combined resistance value of the resistor array 12 becomes a value corresponding to the connection combination of the switch group 13 designated by the combination circuit 14. The oscillation clock 17 (FIG. 4 (c)) output in this manner is used as the oscillation pulse counter 18
Is input to the pulse counting circuit, and the pulse counting is performed here. When the start / stop signal 10 is input, the oscillation pulse counter 18 outputs the count value 27 at that time.

As shown in FIG. 2A, the CRT screen 31
, The character 32 is displayed. In this case, if the value output from the oscillation pulse counter 18 is, for example, m ', the combinational circuit 14 controls the switch group 13 accordingly.

Now, as shown in FIGS. 2A, 2B, and 2C, m pulses are included between the start / stop signals corresponding to both ends of the screen 31, that is, the count value 27. When the frequency of the oscillation clock 17 is set so that is m, the display reference position of the character 32 corresponds to the Mth pulse of the oscillation clock 17. In this case, the combination circuit 14 controls the switch group 13 in such a combination as to decrease the combined resistance value of the resistance array when the count value m ′ output from the oscillation pulse counter 18 is smaller than the above m. . As a result, the frequency of the oscillation clock increases.

On the other hand, the output value m of the oscillation pulse counter 18
When ′ is larger than m, the combination circuit 14 performs combination control of the switch group 13 so as to increase the combined resistance value of the resistance array 12. As a result, the frequency of the oscillation clock is reduced.

By repeating such processing, the frequency of the oscillation clock 17 is kept between the start / stop signals 10 even when the resistance values of the resistance array 12 change due to temperature changes or the like. The switch group 13 is controlled so that m pulses are always included. Therefore, the display reference position (M
The pulse) will also be kept constant.

Next, another embodiment will be described.

FIG. 3 shows a microcomputer with an on-screen display function according to the second embodiment of the present invention. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

In this circuit, the oscillation pulse counter 18 is
The oscillation clock 17 from the oscillator is counted, and the latch pulse 25 is output at the time when counting n pulses preset by software or the like. Where the value "n"
Is set to determine the display position of the character 32 on the screen. The latch pulse 25 is input to the input terminal C _n of the interval timer 24. The interval timer 24 includes a system clock 2 which is a clock serving as a reference for the operation of the microcomputer and having a frequency sufficiently higher than that of the oscillation clock 17.
6 is input as a reference clock from the input terminal C _s . The interval timer 24 counts the system clock 26, outputs K ′ as the count value 33 at the time when the latch pulse 25 is input, and sets it in the control register 28. The combination circuit 14 uses the control register 28.
Based on the value of, the above-mentioned combination control is performed.

In the above embodiment, the connection of each resistor of the resistor array is turned on / off by the switch group to adjust the oscillation frequency. However, the present invention is not limited to this, and a capacitor may be used instead of the resistor array. An array may be provided, and the combined capacitance may be changed by changing the connection combination of the capacitors to adjust the frequency. In addition, the resistor array or the capacitor array,
Of course, not only series connection but parallel connection may be used.

Of course, instead of the combinational circuit 14, program processing by a microcomputer may be performed.

[0025]

As described above, according to the present invention, the combination of the resistor array or the capacitor array is changed so that the oscillation frequency of the character display clock becomes a predetermined number of clocks based on the number of system clocks. Since the adjustment is performed, it is possible to perform automatic adjustment without the need for manual adjustment as in the past. Further, it becomes possible to generate a clock having a stable frequency by following changes in voltage and temperature. Further, since such an oscillator is incorporated in the one-chip microcomputer, it can be easily incorporated in the manufacturing process of the microcomputer, and the cost can be significantly reduced as compared with the conventional LC oscillator. At the same time, there is an effect that it is not necessary to provide the external connection terminal to the microcomputer chip, which has been conventionally required.

[Brief description of drawings]

FIG. 1 is a block diagram showing a microcomputer with an on-screen display function according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an operation of the microcomputer with an on-screen display function.

FIG. 3 is a block diagram showing a microcomputer with an on-screen display function according to another embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an operation of the microcomputer with an on-screen display function of FIG.

FIG. 5 is a block diagram showing a conventional microcomputer with an external CR oscillator and an on-screen display function.

FIG. 6 is a block diagram showing a conventional microcomputer equipped with an LC oscillator and having an on-screen display function.

[Explanation of symbols]

 12 resistor array 13 switch group 14 combinational circuit 18 oscillation pulse counter 24 interval timer 28 control register

Claims (2)

[Claims] 1. A microcomputer having an on-screen display function for displaying character information on a CRT screen so as to be superimposed on an image, the oscillator comprising a resistor array including a plurality of resistors and a capacitor. A switch group for turning on and off the connection of each resistor of the resistor array, a counter for counting the oscillation clock of the oscillator, and a control of an on-off combination of each switch of the switch group according to a count value from the counter And a combination control circuit for controlling the on-screen display function. 2. A microcomputer having an on-screen display function for displaying character information superimposed on an image on a CRT screen, comprising: an oscillator including a capacitor array including a plurality of capacitors and a resistor. A switch group for turning on / off the connection of each capacitor of the capacitor array, a counter for counting an oscillation clock of the oscillator, and a control of an on / off combination of each switch of the switch group according to a count value from the counter. A combination control circuit, and a microcomputer with an on-screen display function.