JPH0667985A - Semiconductor device - Google Patents

Abstract

PURPOSE:To improve a defense function against the unfair reading of a memory in a semiconductor device. CONSTITUTION:The device is provided with a protector 3 having a previously-set code and outputting a protection release signal when the code and a protection release code is coincident and a timer 7 starting time measurement by the input of the protect release code. When a time measured by a timer 7 comes to a set time, an AND gate 8 is prohibited from outputting information from a memory 2 outside without regard to the judging result of coincidence/ noncoincidence by the protector 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device capable of outputting information in a memory when an input protection release code matches a set code.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional semiconductor device, in which 1 is a semiconductor device, 2 is a ROM,
A memory such as EPROM or EEPROM, 3 is a protect device having a preset code, 4 is a semiconductor switch, and a gate is open-controlled by a protect release signal from the protect device 3. Reference numerals 5a and 5b are signal input ports and output ports, and 6a, 6b, 6c and 6d are signal lines.

Next, the operation will be described. Semiconductor device 1
Normally operates on a single chip, but by changing the mode, external access is also possible.
That is, when the information in the memory 2 is read from the outside, the protect release code is input from the input port 5a to the protect device 3 through the signal line 6a, and if this code matches the preset code, the signal on the signal line 6b is reached. Signal becomes active.

Therefore, the semiconductor switch 4 is opened,
The contents of the memory 2 are output from the output port 5b via the signal lines 6c and 6d. If the protection is not released, the semiconductor switch 4 remains closed and the signal line 6
The output of the signal in the memory 2 from c to the signal line 6d is blocked, and the contents of the memory 2 are not output to the outside.

[0005]

Since the conventional semiconductor device is configured as described above, if a password is continuously input a plurality of times, it will accidentally match a preset code. In some cases, the protection device 3 may be able to release the protection, and the information in the memory 2 may be output to the outside.

The present invention has been made in order to solve the above problems, and if an incorrect protect release code is input, if the correct protect release code is not input within a certain time, An object of the present invention is to obtain a semiconductor device that can prohibit the output of information in the memory to the outside.

[0007]

A semiconductor device according to the present invention has a memory storing information and a preset code, and when the code matches a protection release code input from the outside. A protect device for outputting a protect release signal and a time measuring device for starting time measurement by inputting the protect release code, and when the time measured by the time measuring device exceeds a set time, the protect device operates. The AND gate is prohibited from outputting the information from the memory to the outside regardless of the determination result of the match or the mismatch.

[0008]

In the semiconductor device according to the present invention, when a predetermined time elapses after the protection release code is input, the AND gate prevents the output of information from the memory regardless of the output of the protection device.

[0009]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 1 to 6 are the same as those shown in FIG. 2, and thus their duplicated description will be omitted. Reference numeral 7 is a timer as a time measuring device for measuring a preset time, which is set by an external input to the signal line 6a and reset by the output signal of the protector 3 to the signal line 6b.

When the time measurement is completed, the output signal of the timer 7 is "L" → "H" on the signal line 6e.
Stand up. An AND gate 8 inhibits the output of the output signal of the protect 3 by the rising of the output signal of the timer 7, and fixes the signal on the signal line 6f to the "L" state.

Next, the operation will be described. Semiconductor device 1
Normally operates on a single chip, but can be accessed from the outside by changing the mode. Now, when reading the information of the memory 2 from the outside, the protect release code is input from the input port 5a and the content of the memory 2 is output from the output port 5b.

That is, when the protection release code is input from the input port 5a, the timer 7 starts time measurement. If this protection release code matches the preset code, the output signal of the protection device 3 becomes "H", and the output level of the timer 7 is still "L" at this time, so the semiconductor switch 4 Is opened, and the contents of the memory 2 are output to the output port 5b via the signal lines 6b and 6c. At this time, the timer 7 is reset by the output of the protection device 3.

On the other hand, if there is an erroneous input from the input port 5a, the input of the protect release code from the input port 5a is again required, but the timer 7 continues to measure the time and keeps a certain value. When time passes, timer 7
Output rises to "H", and thereafter, even if the protection release code matches the preset code and the output signal of the protection device 3 becomes "H", the semiconductor switch 4 remains closed. Therefore, the information in the memory 2 is not output to the outside.

Example 2. In the above embodiment, the case where the timer 7 is used as the time measuring device has been described, but an integrating circuit composed of a capacitor and a resistor may be used, and the same effect as that of the above embodiment can be obtained.

[0015]

As described above, according to the present invention, when a memory for storing information and a preset code are provided and the code and the protect release code inputted from the outside are matched, A protect device for outputting a protect release signal and a time measuring device for starting time measurement by inputting the protect release code are provided, and when the time measured by the time measuring device exceeds a set time, the protect device operates as described above. Since the AND gate is configured to prohibit the output of the information from the memory to the outside regardless of the determination result of the match and the mismatch,
There is an effect that it is possible to more reliably prevent the information in the memory from being output by unauthorized release of protection, and to realize this with a simple circuit configuration at low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional semiconductor device.

[Explanation of symbols]

 2 memory 3 protect device 7 timer (time measuring device) 8 and gate

Claims (1)

[Claims] 1. A protect device having a memory for storing information, a preset code, and which outputs a protect release signal when the code matches a protect release code inputted from the outside, A time measuring device that starts time measurement by inputting a protection release code, and when the time measured by the time measuring device has passed a set time, the memory is irrelevant regardless of the result of the match or non-match determination by the protect device. A semiconductor device including an AND gate that prohibits output of information from the outside to the outside.