JPH02108095A - Output circuit for liquid crystal display - Google Patents

Abstract

PURPOSE:To eliminate the through-current of an output transistor of a liquid crystal display circuit which is not used and to contrive the reduction of power consumption by setting the value of an output signal to a fixed value by the value of a rewritable register. CONSTITUTION:When the contents of a programmable register 6 are '1', '1' is inputted to the input (b) of a 2-AND circuit 3, and the input (d) of the 2-AND circuit 3 and the signal of an output (a) become the same waveform. Subsequently, when the contents of the programmable register 6 are '0', that is, in the case of (b) = '0', the output of the 2-AND circuit 3 is fixed to '0' irrespective of the signal (d). Therefore, a P channel transistor 4 conducts, an N-channel transistor 5 becomes non-conducting, and V1 is outputted from an output terminal 7. In such a manner, the output of a liquid crystal display output terminal which is not used is fixed by the value of the register, an unnecessary current consumption is eliminated and the low power consumption is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output circuit for a liquid crystal display that is self-selected for a one-chip microcomputer.

[Conventional technology]

FIG. 3 is a circuit diagram showing a conventional output circuit for liquid crystal display. In the figure, (1) a register that indicates whether to light up the liquid crystal corresponding to ti, (2) an exclusive OR circuit, (4) a liquid crystal drive I@P channel transistor, and (5) a liquid crystal drive. N-channel transistor for (
7) is the output terminal -vl ev2, which is a liquid crystal power supply circuit.

Next, the operation tc)Ln will be explained. Register (1) is a data latch that completely determines whether or not to turn on the liquid crystal.

This data (e) determines the waveform output from the output terminal (7). The case where the contents of register (1) is -1" will be explained. If the data e is 1" and the signal C (liquid crystal display output control signal) has the waveform shown in Fig. 2, the exclusive OR output Output d# of (2):
This rounding will result in a waveform as shown in the figure.

The final waveform at the output terminal (7) is as shown in the figure. Furthermore, when the data Jr8 of the register J (1) is 10'', the signal dFi is e=
The phase is opposite to that of 11v'. Therefore output terminal (7)
As shown in FIG. 2, the output signal of is in the opposite phase to the output signal of the output terminal (7) when e=v'1#.

Here, the liquid crystal display output waveform is changed over a certain period (t in Fig. 2).
The reason why the output level changes from high level to low level (shown with This is to prevent this.

Generally, signals for liquid crystal display are set so that the voltage changes over a certain period of time.

[Problem to be solved by the invention]

Conventional liquid crystal display output circuits are configured as described above, so the output signal always changes even if the liquid crystal display terminal is not in use.

There is a problem in that a through current flows through the output transistor, resulting in unnecessary current consumption.

This invention was made to solve the above-mentioned problems, and its purpose is to eliminate the through current of the output transistor of an unused liquid crystal display circuit, thereby reducing current consumption. .

[Means to solve the problem]

The output circuit for a liquid crystal display according to the invention is configured to keep the value of an output signal constant based on the value of a rewritable register, and eliminate the through current flowing through the output transistor.

[Effect]

The output circuit for a liquid crystal display according to the present invention logically controls the gate signal of the output transistor according to the value of a rewritable register, and fixes the output signal value to reduce the through-current flowing through the output transistor. It was designed to eliminate it.

〔Example〕

Hereinafter, one embodiment of the invention (17) will be described with reference to the drawings. In Figure 1, (1) is a data latch that determines whether or not all LCDs are lit, (2) is an exclusive OR circuit, (6) is a programmable register, and (3) is the output of programmable register (6). (b) A 2-AND circuit whose input is the output of the exclusive OR circuit (2).

(4) and (5) connect the 2 AND output of the AND circuit (3) to the gate input. P-channel and N-channel transistors, (7) is the output terminal.

Next, the operation will be explained. First, when the content of the programmable register (6) is V'''1, "1" is input to the input (1) of the 2AND circuit (3), so
The input signal and output a signal of the 2A N D circuit (3) have the same waveform.

Therefore, when b=ゝ'1'', the operation is the same as the conventional output circuit shown in Figure @3.0 Next, the contents of the programmable register (6) are ``□ II
The case will be explained below. If b=1'0'', 2AN
The output of the D circuit (3) is fixed at '0' regardless of the signal d. Therefore, the P-channel transistor (4) becomes conductive, and the N-channel transistor (5) becomes non-conductive.

vl is output from the output terminal (7). in this way.

b: In the case of "0", the output potential is fixed, and there is no through current between vl and v2 that flows when the output potential changes.

〔Effect of the invention〕

As described above, according to the present invention, the output of the unused LCD display output terminal can be fixed by the value of the register, and by eliminating unnecessary current consumption, it is possible to completely reduce power consumption. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an output circuit for a liquid crystal display according to an embodiment of the present invention, FIG. 2 is a signal waveform diagram, and FIG. 3 is a circuit diagram of a conventional output circuit for a liquid crystal display. In the figure, (1) is a data latch, (2) is an exclusive OR circuit, (3) is a 2AND circuit, and (4) is a P
Channel transistor (5) is an N-channel transistor. (6) is a programmable register, and (7) is an output terminal. In Figure 1, the same symbols indicate the same or equivalent parts〇

Claims (1)

[Claims] The output of a logic circuit that receives as input the data signal for driving the liquid crystal of a microcomputer with a built-in liquid crystal driving circuit and the output signal from the programmable register is used as a second data signal for the liquid crystal display. The drive circuit for the LCD display is operated by the programmable register value, regardless of whether the LCD is turned on or off.
An output circuit for a liquid crystal display, characterized in that a second data signal can be fixed.