JPS6370450A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To use one terminal as a segment output terminal and also as a computer input terminal, by providing a function switching circuit, which can set the active state and the inactive state of a segment output function and a computer input function, which are connected to a common terminal. CONSTITUTION:In a single chip microcomputer 7, segment output driving circuits 4l-4n are set at a high output impedance state when a function switching signal 5 is set at an (input) as hardware or set at the (input) with an initialization routine of software at the time of reset. The logic value of the external input, which is applied on terminals 30n-30l, is read through an input circuit 6. When input terminals 3l-3n are not required and this circuit is used in a system, in which (n) pieces of segments are provided in a liquid crystal display device, the function switching signal 5 is initially set at a (segment output) with software. Thus the system can be operated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to CMOS digital circuits.

[Conventional technology]

Figure 3 shows a CM with a conventional liquid crystal display drive circuit.
It is a block diagram showing an OS single-chip microcomputer, in which 1 is a liquid crystal display device drive circuit, 2
a~2d are common output terminals for driving the liquid crystal display device; 3a~
31 to 3n are segment output terminals for driving the liquid crystal display device;
7 is a CMOS single-chip microcomputer having a liquid crystal display drive circuit 1; 8 is an externally connected liquid crystal display; 9 is another peripheral circuit; 10a is a general input/output circuit that connects the peripheral circuit 9 and the microcomputer 7; wiring, 1
0b is a general input wiring, 10c and 10d are signal lines that send signals from the peripheral circuit 9 to the microcomputer 7, and 11 is a multiplexer that connects the signal lines 10c and 10d together to the line 10b.

Next, the operation will be explained.

The liquid crystal display device is the common output 2 of the microcomputer 7.
a to 2d and segment outputs 3a to 31. Since the segment output terminals 3i+1 to 3n are not used, they are left unconnected.

On the other hand, since the peripheral circuit 9 has a large number of signal lines to be exchanged with the microcomputer 7, the multiplexer 11 is used to increase the number of input signal lines to the microcomputer 7.

[Problem that the invention seeks to solve]

A conventional CMOS single-chip microcomputer with a liquid crystal display drive circuit is configured as described above, so when building a system using this, even though there are extra segment output terminals for driving the liquid crystal display, However, there have been problems in that the number of input terminals is insufficient, or conversely, there is a surplus of input terminals but a shortage of segment output terminals for driving the liquid crystal display device. The above conventional example is an example in which the number of external circuits and multiplexers has increased because the number of input terminals is insufficient.

This invention was made to solve the above-mentioned problems.Instead of requiring fewer segment output terminals for driving a liquid crystal display device, it is possible to reduce the number of input terminals from a system that requires a microcomputer with many input terminals. However, the present invention aims to provide a CMOS single-chip microcomputer that can be used in systems that require a microcomputer equipped with many segment output terminals for driving a liquid crystal display device.

[Means for solving problems]

A semiconductor integrated circuit according to the present invention is a CMOS single-chip microcomputer having a liquid crystal display device driving circuit, in which a segment output terminal of the liquid crystal display device driving circuit and a terminal of an input circuit are shared, and a segment output terminal connected to the shared terminal is provided. A function switching circuit is provided that can set the active/inactive state of the function and computer input function.

[Effect]

In this invention, the segment output terminal of the liquid crystal display drive circuit and the terminal of the input circuit are shared, and the function switching circuit is capable of setting the active or inactive state of the segment output function and the computer input function connected to the shared terminal. Because of this provision, one terminal can be used both as a segment output terminal and as a computer input terminal depending on the settings.

〔Effect of the invention〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a liquid crystal display device drive circuit, 2a to 2d
is a common output terminal for driving a liquid crystal display device, 3a to 3 are segment output terminals for driving a liquid crystal display device, and 301 to 30n are segment output terminals for driving a liquid crystal display device.
41 to 4n are segment output drive circuits with function switching circuits, 5 is a function switching signal, 6 is an input circuit, and 7 is a CMOS single having a liquid crystal display drive circuit 1. A chip microcomputer, 8 an externally connected liquid crystal display device, 9 other peripheral circuits, and 10 a peripheral circuit 9
This is general input/output wiring connecting the microcomputer 7 and the microcomputer 7.

Next, the operation will be explained.

This single-chip microcomputer 7 can be configured as a system as shown in FIG. can correspond to

At this time, the segment output drive circuits 41 to 4n receive the "input" setting instruction from the function switching signal 5 and are in a high output impedance state. Terminals 30n~30j! The logic value of the external input applied to can be read through the input circuit 6.

In the case of FIG. 1, the number of segment terminals is less than the number of segment terminals of the liquid crystal display device 8, but as shown in FIG.
Let us consider a case in which the present invention is used in a system in which a liquid crystal display device does not require a single segment and has one segment of a liquid crystal display device. This can be handled by initially setting the function switching signal 5 to "segment output" using software. When the initial setting is performed in this manner, the segment output drive circuits 41 to 4n with function switching circuits are put into the output state. Although the input circuit 6 is not operated, if a through current flows depending on the circuit system, it is possible to suppress this by using the function switching signal 5. In the above embodiment, one function switching signal 5 is shown, but two signals may be provided to switch the number of segments to large, medium, or small, or three or more may be provided to enable more fine-grained switching. .

〔Effect of the invention〕

As described above, according to the inventor, the segment output terminal is shared with the computer input terminal, and a function switching circuit that can set the active or inactive state of these output functions and input functions is provided, so that the segment output terminal can be used for driving a liquid crystal display device. Compatible with systems ranging from systems that require a microcomputer with fewer segment output terminals but many input terminals to systems that require fewer input terminals but require a microcomputer with many segment output terminals for driving the liquid crystal display device. This has the advantage of being able to provide a CMOS single-chip microcomputer with high performance.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a system using a CMOS single-chip microcomputer having a liquid crystal display device driving circuit according to one embodiment of the present invention, and FIG. 2 is a conceptual diagram of a system showing another embodiment of the present invention. FIG. 3 is a conceptual diagram of a system using a CMOS single-chip microcomputer with a conventional liquid crystal display driving circuit. 1 is a liquid crystal display device drive circuit, 2a to 2d are common output terminals for driving the liquid crystal display device, 3a to 31 to 3 to 3n are segment output terminals for driving the liquid crystal display device, and 301 to 30n are segment output terminals and computer input terminals. , 41-4
n is a segment output drive circuit with a function switching circuit, 5
is a function switching signal, 6 is an input circuit, 7 is a CMOS single-chip microcomputer, 8 is a liquid crystal display device,
9 is other peripheral circuit, 10 is general input/output wiring, 10a
is general input/output wiring, 10b is general input wiring, 10
C and 10d are signal lines, and 11 is a multiplexer.

Claims (1)

[Claims] (1) In a CMOS single-chip microcomputer having a liquid crystal display device driving circuit, a terminal to which all or some of the plurality of liquid crystal driving segment outputs and all or some of the plurality of microcomputer inputs are commonly connected; A semiconductor integrated circuit comprising: a liquid crystal driving segment output function connected to the terminal; and function switching means for setting an active/inactive state of a computer input function.