JPS63317869A - Action mode control circuit - Google Patents

Abstract

PURPOSE:To obtain a single-chip microcomputer having an action mode which is opened to users by increasing the action mode to be set without increasing the number of terminals. CONSTITUTION:In case the output signal levels a2 and a3 of flip-flops 4 and 5 are initialized at low values after reset initialization, the value of a chip 3 is set at (000) or (100) after the reset initialization (a1, a2, a3) based on the input level of a control signal. Then a ROM extension mode can be defined with (a1, a2, a3)=(100) as long as a single-chip mode is defined with (a1, a2, a3)=(000). Then it is possible to obtain four types action modes (001), (101), (011) and (111) that are available with a manufacturer only when a flip-flop 5 is set at a high level (unopened) by a program and the output signal of a3 is set at a high level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an operation mode control circuit for a semiconductor integrated circuit of a single-chip microcomputer.

2. Description of the Related Art As the field of application of single-chip microcomputers expands, the operational forms in which they are used are diversifying. For example, when using a single-chip microcomputer alone, when using it by connecting an external ROM or RAM, etc., and in addition to the operation mode used by the user, the manufacturer There are also operating modes used to test integrated circuits. In this way, a single-chip microcomputer has a plurality of operating modes depending on the purpose of use.

Switching between these multiple operation modes is performed by applying a control signal to a specific signal input terminal, but the operation mode setting used by the user can be easily set, and the operation mode setting used by the manufacturer is It is desirable that the user cannot easily make settings. In particular, single-chip microcomputers often have an operating mode that inspects the contents of the ROM integrated inside the chip, but from the standpoint of software protection, such an operating mode cannot be easily set by the user. It is preferable not to have it.

Conventionally, the operation mode setting method often used is to provide k signal input terminals for operation mode control, input high-level or low-level signals to each terminal, and decode these signal levels. 2
There is a method that allows setting of k different operating modes.

FIG. 2 is an example of a functional block diagram when two operation mode control signal input terminals are used. 1.2 is a control signal input terminal, and 3 is a decoder for decoding the signal levels of the two terminals and generating signals necessary for each operation mode. In this example, there are 22=4 combinations of setting the two control signal input terminals to high level or low level, and it is possible to set a maximum of four operation modes.

Problems to be Solved by the Invention In the conventional operation mode control circuit as described above, the advantage is that the user can easily specify the desired operation mode by simply setting the control signal input terminal to high or low level. However, as the total number of operating modes increases, the number of control signal input terminals must also increase. This point is disadvantageous for manufacturers in terms of cost and performance of single-chip microcomputers, and furthermore, the operating mode for testing semiconductor integrated circuits can be easily set by the user. There is a drawback.

The present invention solves the above-mentioned problems by making it possible to set multiple operation modes without increasing the number of control signal input terminals, and moreover, the operation modes used by the manufacturer can be easily set by the user. The purpose of the present invention is to provide an operation mode control circuit for a single-chip microcomputer that cannot be used.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for controlling the signal levels of k control signal input terminals and the outputs of n flip-flops that can be set to high or low levels by a program. The device is equipped with a decoder for decoding levels and generating signals necessary for each operation mode, and a maximum of 2 (k+n) operation modes can be set using k control signal input terminals.

Effects According to the present invention, many operation modes can be set without increasing the number of control signal input terminals.

In addition, since the output level of the flip-flop is set by a program, the programming method for setting the operating mode used by the manufacturer is not disclosed to the user, making it difficult for the user to easily set the operating mode used by the manufacturer. can do.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. This example has one control signal input terminal 1 and two flip-flops 4 and 5 whose output level can be set by a program.
This figure shows the configuration of an operation mode control circuit for a single-chip microcomputer that can generate up to 23 (=8) types of operation mode signals using a decoder. In the following explanation, the operation modes used by the user will be briefly explained as single-chip mode, which is commonly used in single-chip microcomputers, ROM expansion mode, and R
The following describes four cases: AM expansion mode and ROM-RAM expansion mode.

In the present invention, since the operation mode is switched by a program, after the chip is reset and initialized, the internal R
The setting of the operating mode as to which program is executed in the OM or the external ROM is determined by the output level a1 of the control signal input terminal 1 shown in FIG. For example, 7 lip flops 4 and 5 after reset initialization.
The output signal level a2. If the initial setting of a3 is low level, after the chip is reset and initialized (a + a2a
The value of 3) will be (000) or (100) depending on the level of the control signal input, and <a+ aza3) = (000
) is a single-chip mode, then (a+
When az a:+)=(100), the mode is ROM expansion mode. After this reset initialization of the ROM operating mode, the level of the flip-flop is set by a program and the RAM operating mode is determined. If this setting is determined by the value of the output a2 of the flip-flop 4, if (a+ az az) = (010), R
AM extended mode, (a+82 az)=(11
0), it becomes ROM-RAM expansion mode. As described above, the allocation of the four operation modes used by the user has been determined, and the next allocation of the operation modes used by the manufacturer is to set the flip-flop 5 to a high level by a program and to Set by setting the level to high level (a+ az az)
-(001).

Up to four different operation modes (101), (011), and (111) can be assigned.

Unless the high level setting method of the flip-flop 5 is disclosed to the user, the user cannot easily set it to the operating mode used by the manufacturer. Although the above example shows the case of one control signal input terminal, in general, if there are k control signal input terminals, 2k operation modes can be set after the chip is reset and initialized. The RAM operation mode is also determined in the initial settings.
It is also possible to switch the operating mode of the RAM later by a program.

Effects of the Invention As described above, according to the present invention, it is possible to increase the total number of operation modes that can be set for a single-chip microcomputer without increasing the number of control signal input terminals for determining the operation mode. . Further, by providing a flip-flop for switching to the operation mode used by the manufacturer, which is not disclosed to the user, it is possible to prevent the user from easily setting the operation mode to the operation mode used by the manufacturer.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional embodiment. 1.2... Control signal input terminal, 2...
Decoder, 4.5...Flip-flop. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1

Claims (1)

[Claims] It decodes the signal levels of k control signal input terminals for determining the operation mode and the output levels of n flip-flops that can be set to high or low level by program, and generates the signals necessary for each operation mode. In addition to the 2^k operation modes determined by reset initialization of the microcomputer through the k control signal input terminals, the flip-flop determines an additional 2^n operation modes. What is claimed is: 1. An operation mode control circuit characterized in that the operation mode control circuit is equipped with a maximum of 2^(^k^+^n^) types of operation mode signal generation means.