JPH0380318B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an electronic device that can drive both a cathode ray tube (hereinafter referred to as CRT) and a liquid crystal display (hereinafter referred to as LCD).

(b) Prior Art Among conventional personal computers, portable ones that use an LCD as a display and can be powered by batteries have been developed, as shown in Japanese Patent Laid-Open No. 59-91524, for example. It is very convenient as it can be used outdoors. However, LCD
Because it is smaller and has less display capacity than CRT, when using CRT indoors, it is better to use LCD.
Due to the difference in CRT display configuration, an expansion device had to be connected to drive the CRT, making the device larger. However, recently it corresponds one-to-one with CRT.
With the development of LCDs and drive ICs that can drive both CRTs and LCDs, it has become possible to drive CRTs without connecting an expansion device.
In this case, it is pointless to drive both the CRT and the LCD at the same time, and it is not preferable in terms of power consumption in portable and battery-powered devices.

(c) Problems to be solved by the invention The present invention has been made in view of the above problems.
When it detects that a CRT is connected, the built-in
The present invention provides an electronic device configured to prohibit driving of an LCD.

(d) Means for Solving the Problems The present invention comprises means for detecting that a CRT is connected, and means for prohibiting LCD driving and cutting off power to the LCD upon detection of the CRT connection. It is something.

(e) Effect Since the present invention is configured as described above,
When a CRT is connected, driving of the built-in LCD is prohibited.

(f) Examples An embodiment of the present invention will be described below with reference to the drawings.

The figure shows the configuration of a portable personal computer. Reference numeral 1 denotes a control circuit composed of a microprocessor, which performs overall control according to a program in a program memory 2 in which processing programs are stored in advance. Reference numeral 3 denotes a memory for storing data input from the keyboard 4 or data processed by the control circuit 1, and writing and reading of data is controlled by the control circuit 1. 5 is LCD
This drive circuit is capable of driving both the CRT and the CRT, and exchanges display data with the video memory 6, and outputs the display data to the LCD output buffer circuit 7 and the CRT output buffer circuit 8. video memory 6
It has a memory capacity that corresponds one-to-one with the display dots of the LCD and CRT, and is configured so that the display can be changed by rewriting data in the video memory 6. The LCD output buffer circuit 7 and the CRT output buffer circuit 8 receive an enable signal (,
Drive control is performed by CRTEN).
Reference numeral 10 denotes an LCD to which output data from the LCD output buffer circuit 7 is supplied, and is constituted by a display of, for example, 600 x 200 dots. 11 is a connector to which the CRT 12 shown in FIG. 3 is connected, and R, G, B signals, etc. from the CRT output buffer circuit 8 are supplied thereto. 13 is a detection circuit connected to the output of the CRT output buffer circuit 8, and is connected to the connector 11.
It detects whether or not the CRT 12 is connected, and supplies the detection output to the input/output interface circuit 9. 14 is a power control circuit that controls power supply to the LCD 10 based on the CRT enable signal (). The control circuit 1 includes signal buses 15 such as an address bus, a data bus, and a control bus.
It is connected to each part and sends and receives signals.

FIG. 2 is a diagram showing the detection circuit 13, showing the R signal of the R, G, and B signal output of the CRT output buffer circuit 8, and 16 is a voltage detection whose input is supplied with a divided voltage by resistors 17, 18, and 19. The threshold voltage is set to 1.2V on the device. Connector 11
When the CRT12 is not connected to the resistor 17,
18 and 19, the input voltage of the voltage detector 16 is approximately
Since the voltage is 0.6V, which is lower than the threshold voltage of 1.2V, the voltage detector 16 outputs an H level signal. Note that 20 is a switch that forcibly sets the output of the voltage detector 16 to a low level.

FIG. 3 is a diagram showing the configuration of a typical input circuit of the CRT 12, in which a voltage of about 2.9 V is applied to point A of the R signal input by resistors 21 and 22. Although the drawing shows the case of an R signal, a G or B signal may also be used.

FIG. 4 is a diagram showing the configuration of the power supply control circuit 14.
-12V voltage is applied to LCD1 through transistor 23.
0, low level
It is controlled via an inverter 25 so that the control transistor 24 becomes non-conductive when the CRT enable signal (CRTEN) is supplied, and the control transistor 24 controls the transistor 23 so that the LCD
The controller 10 is configured to control power supply to the controller 10.

Next, the operation of the present invention having such a configuration will be explained.

First, when a power switch (not shown) is turned on, the control circuit 1 performs an initial clear process according to the program in the program memory 2. At this time, the control circuit 1 checks the signal of the input/output interface circuit 9 and clears the signal from the detection circuit. The signal from 13 is detected.

Assuming that the CRT 12 is not connected now, the output of the voltage detector 16 of the detection circuit 13 shown in FIG. A low level LCD enable signal () is supplied to the LCD output buffer circuit 7 via the input/output interface circuit 9. At this time, the CRT enable signal () is set to high level, so that the CRT output buffer circuit 8 is disabled and the CRT enable signal () is set to high level.
The power supply control circuit 14 shown in FIG.
The control transistor 24 is turned on by the output of 5, and the transistor 23 is turned on, so that the LCD
A driving voltage of -12V is supplied to 10. In this way, the data input from the keyboard 4 and the data processed by the control circuit 1 are transferred to the drive circuit 5.
and video memory 6 as display data on the LCD
By being supplied to the LCD 10 via the output buffer circuit 7, a display is performed on the LCD 10.

Next, we will explain the operation when a CRT is connected.

When the power switch is turned on after connecting the CRT 12 to the connector 11, the control circuit 1 checks the signal of the input/output interface circuit 9 and detects the signal of the detection circuit 13 in the initial clear process as described above. . In this case, the voltage at point A of the CRT 12 is supplied to the voltage detector 16 of the detection circuit 13, as shown in FIG.
is much larger than the resistance 21 of CRT12,
Approximately 1/2 of the potential at point A is input to the voltage detector 16.
1.5V supplied, threshold voltage 1.2V
Because of the above, the output of the voltage detector 16 is set to low level. Upon detection of the low level signal, the control circuit 1 determines that the CRT 12 is connected, and, contrary to the above, sets the CRT enable signal () to a low level and sets the LCD enable signal () to a high level. As a result, the CRT output buffer circuit 8 is set to an active state, and the LCD output buffer circuit 7 is set to an inactive state. In this way, the display data output from the drive circuit 5 is supplied to the CRT 12 via the CRT output buffer circuit 8 and displayed.

At this time, the output of the LCD output buffer circuit 7 is
Although it is in a high impedance state, if noise occurs in the signal line, a meaningless display due to the noise may be displayed on the LCD 10. Therefore, in this application, the CRT enable signal () becomes low level and is supplied to the power supply control circuit 14, thereby making the control transistor 24 non-conductive and the transistor 23 non-conductive, thereby cutting off the drive voltage (-12V) to the LCD 10. This prevents unnecessary display from occurring due to noise.

The input circuit of CRT12 is as shown in Figure 3.
If it is not pulled up to the power supply by resistors 21 and 22 and a voltage of approximately 2.9V is not generated at point A, the output of the detection circuit 13 will not go to low level even if the CRT 12 is connected to the connector 11. Therefore, in the case of such a CRT12, switch 2
Forcibly set to low level by closing 0,
Instruct to connect CRT12.

In addition, in the embodiment, the connection of the CRT 12 is automatically detected based on the voltage change of the signal line of the CRT output buffer circuit 8, but in another embodiment, the connector of the CRT 12 can be connected to the connector 11. It is also possible to provide a switch that is closed and to detect it mechanically.

Further, although the embodiments have been shown in the case of a personal computer, the present invention can also be applied to other electronic devices such as word processors.

(g) Effects of the invention As described above, the electronic device of the present invention has a common video memory and a drive circuit, is configured to be able to drive both an LCD and a CRT, and is provided with means for detecting that the CRT is connected. , prohibits driving of the built-in LCD when it is detected that a CRT is connected,
This reduces power consumption and prevents unnecessary displays from being displayed on the LCD due to noise, etc.
This is useful for battery-powered electronic devices with large built-in LCDs.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the electronic device of the present invention, FIG. 2 is a circuit diagram showing the configuration of the detection circuit in FIG. 1, FIG. 3 is a circuit diagram showing the main parts of a CRT, and FIG.
1 is a circuit diagram showing the configuration of the power supply control circuit of FIG. 1. FIG. 1...Control circuit, 2...Program memory, 3
...Memory, 4...Keyboard, 5...Drive circuit, 6...Video memory, 7...LCD output buffer circuit, 8...CRT output buffer circuit, 9...
...I/O interface circuit, 10...LCD.
12...CRT, 13...detection circuit, 14...power control circuit.

Claims (1)

[Claims] 1. In an electronic device configured to selectively drive both a built-in LCD and an externally connected CRT using a common drive circuit and video memory,
1. An electronic device comprising: means for detecting that a CRT is connected; and means for inhibiting driving of an LCD upon detection by the means.