JPS61148378A - Single chip microcomputer - Google Patents

Abstract

PURPOSE:To enable a test mode control simply without setting a testing terminal, by detecting a specified voltage fed to a terminal for oscillator to output a test mode signal from a voltage detection circuit. CONSTITUTION:An oscillation element 13 is connected to the oscillator input and output terminals Xin and Xout of a chip 11 of a single chip computer to generate a clock from an oscillator 12 while the normal power source voltage is detected with a voltage detection circuit 14, from which an L signal is outputted to be a normal mode specifying signal. On the other hand, when a specified voltage such as high voltage is applied to the terminal Xin from a high voltage generation circuit 15 or the like, it is detected with the circuit 14, the output of which is inverted to H to be a test mode specifying signal. Here, the clock from a clock signal source 16 in which the output impedance connected to the terminal Xout is lower than the oscillator 12 is fed to the computer. Thus, a single chip microcomputer can be tested simply without providing a testing terminal or the like.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention improves the test mode setting means to improve the RO
The present invention relates to a single-chip microcomputer that allows tests such as checking the contents of M and the execution of instructions to be easily performed.

[Background Art] In a single-chip microcomputer, in addition to the modes normally used by the user, it is necessary to perform tests such as checking the contents of the ROM stored in the microcomputer and the execution of instructions. It is. In order to execute such a test, a test mode is set. In order to set this test mode, it is necessary to supply a test mode command signal to the microcomputer. be.

In order to set up such a test mode for a microcomputer, for a single chip element,
A test bin for supplying and coupling the test mode command is specially set, and a command signal is set to be supplied to this test bin. However, if the test bin is set up in this way, one terminal will be exclusively used for this test mode, which is not effective for microcomputers with a limited number of terminals. It's not something.

It has also been considered to specify some input terminals, to latch the states of the input/output terminals in the reset state, and to determine the test mode based on the latched contents. However, such means are not effective because the input/output terminals used for testing are limited in the process of use by the user.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned points, and it is possible to solve the problem without setting special test terminals for the microcomputer, and without setting special input/output terminals. It is an object of the present invention to provide a single-chip microcomputer that allows the test mode to be easily set and controlled without the need for troublesome operations such as determining and using the state.

[Means for solving the problem] That is, in the single-chip microcomputer according to the present invention, a specified voltage different from a normally used voltage value is detected for the oscillator terminal. A voltage detection circuit is connected and set, and when a signal of the specified voltage value is coupled to the oscillator terminal instead of the oscillation element, a test mode signal is output from the voltage detection circuit. This is how it was done.

[Function] In the microcomputer described above, the contents of the ROM and the execution of instructions can be controlled by supplying and setting a specified voltage signal to the oscillator terminal used in normal operating conditions. A test mode is set to execute tests such as confirmation, and especially for the terminals of such single-chip microcomputers,
The test mode can be effectively executed without making any improvements. In this case, the output terminal of the oscillator may be used to externally supply and set a clock signal for causing the microcomputer to execute the test mode.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a portion corresponding to an oscillator, and a chip 11 of this microcomputer is equipped with an oscillator 12 that generates a clock signal. An oscillation element 13 made of crystal or the like is connected to this oscillator 12, and this oscillation element 13 is connected to the chip 11.
is set externally to the input terminal Xin of the oscillator 12.
and output terminal X0IJt. The oscillator 12 generates a system clock signal used for internal arithmetic processing and the like.

Further, a voltage detector 14 is set in the chip 11. This voltage detector 14 detects Vdd when the signal normally used in the arithmetic processing of this microcomputer is formed by a negative logic signal based on Vdi.
It is configured to detect a signal with a higher voltage value than 1, or it is configured to detect a signal with a voltage value lower than VSS. The input terminal section of this voltage detector 14 is connected to the input terminal Xin to which the oscillation element 13 is connected.

When a voltage signal with a value higher than Vdd set by the voltage detector 14 is set to be supplied to this input terminal Xin, or when a voltage signal with a value lower than VSS is set to be supplied, this voltage signal is A test mode signal is generated upon detection, and a normal mode signal is generated when the voltage signal is not supplied as described above and the normal operation is in a normal operation state.

That is, when a user normally uses this microcomputer, the oscillation element 13 is connected between the oscillator input/output terminals Xin and )(out, and the oscillator 1
2 generates a clock signal of a predetermined frequency, and arithmetic processing is executed by a program set by the user. In this case, since the voltage signal set by the voltage detector 14 is not supplied to the input terminal Xin, the output signal from this detector 14 is at a low level, and this microcomputer normally mode and never set to test mode.

On the other hand, when setting the test mode, the second
As shown in the figure, a high voltage signal serving as a test mode command signal is supplied from a high voltage generation circuit 15 to the input terminal Xin to which the oscillation element 13 is connected. in this case,
The test mode command signal is composed of a signal with a voltage value higher than the voltage Vdd, and the voltage detector 14 is set to output a test mode signal when a voltage signal higher than Vdd is input. has been done. Therefore, as described above, the high voltage generation circuit 1 generates a test mode signal with a voltage value higher than Vdd to the input terminal.
By connecting and setting 5, a test mode signal is generated from the voltage detector 14. This test mode signal is supplied as a test mode setting command to the arithmetic processing circuit set inside the chip 11, and a predetermined test is executed to evaluate this microcomputer. be.

When set to such a test mode, a clock signal is supplied to the output terminal Xout of the oscillator 12 from an external signal source 16 whose impedance is lower than the output impedance of the oscillator 12, and this clock signal A test calculation operation is executed in a test mode inside the chip 11.

Note that the voltage detector 14 that detects an input signal of a voltage higher than the Vdd is an analog voltage comparator, but as shown in FIG. 3, a plurality of transistors 17a, 17b, . ... are set in series, and the threshold voltages of these transistors 17a, 17b, ... are used to connect the input terminal x.
The test mode signal may be output when a high voltage signal higher than a predetermined value is supplied to tn.

Further, in the above embodiment, a case has been described in which the test mode command signal is constituted by a signal with a voltage value higher than Vdd, but this test mode command signal may be constituted by a signal with a voltage value lower than VSS. . In such a case, the voltage detector 14 is configured to output a test mode signal when a signal with a voltage value lower than VSS is input. In this case, the high voltage generation circuit 15 is constituted by a low voltage generation circuit that generates a test mode command voltage signal having a value lower than Vss.

[Effects of the Invention] As described above, in the single-chip microcomputer according to the present invention, there is no need to set a special input terminal for setting the test mode, and there is no need to set a special input terminal for the input/output terminal. The test mode can be effectively set by the input terminal for connecting and setting the normally existing oscillation element without imposing any restrictions. Therefore, in this microcomputer, there is no need to increase the number of input/output terminals corresponding to the test mode, and the microcomputer can be configured to be extremely easy to use for the user.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the configuration of a single-chip microcomputer according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the configuration when the microcomputer is set to a test mode, and FIG. FIG. 2 is a circuit diagram showing an example of the configuration of a voltage detector set to . DESCRIPTION OF SYMBOLS 11... Chip, 12... Oscillator, 13... Oscillation element, 14... Voltage detector, 15... High voltage generation circuit, 16... Clock signal @ source.

Claims (1)

[Claims] A voltage detection circuit that detects the input of a specified voltage different from the normally used voltage value is set for the input terminal connected to the oscillation element set externally, and the input terminal is supplied with a voltage signal corresponding to the voltage value specified above in the test mode setting command state, and when this voltage signal is supplied, the test mode is set from the voltage detection circuit. A single-chip microcomputer characterized by outputting a signal.