JP2953713B2 - Semiconductor integrated circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit, and more particularly to a semiconductor integrated circuit including a test circuit for a counter.

[Conventional technology]

Generally, in a semiconductor integrated circuit, a counter is often used as a component thereof, and in addition, as the size of the semiconductor integrated circuit increases, a counter having a large count may be used. Therefore, a test circuit for confirming the function of the counter itself is required, and the test circuit is usually inserted and provided inside the semiconductor integrated circuit. In this case, the larger the counter, the larger the number of test patterns required to confirm all functions.To shorten this test pattern, the large-count counter is divided into small-count counters. And perform functional tests.

FIG. 3 is a block diagram showing an example of a conventional semiconductor integrated circuit.
And a test circuit 14 including OR circuits 15 to 17.

In FIG. 3, when the function test of the counter 9 is performed, each of these counters 10 to 13 included in the counter 9 with a small number of counts is separated in accordance with the input of the clock signal 104. On the input side of the carry signal at, input the corresponding outputs of the OR circuits 15 to 17 that take the logical sum of the output of the carry signal of the previous stage counter of each counter and the control signal 105 input from the outside,
The function test is performed by switching the control signal 105.

[Problems to be solved by the invention]

In the above-described conventional semiconductor integrated circuit, as a test circuit of the counter, the counter is divided into small counters and the function test is performed individually, but in this method, the counter before the division is divided. There is a disadvantage that the original function cannot be confirmed.

[Means for solving the problem]

The semiconductor integrated circuit of the present invention has at least a counter and a test circuit that performs a function test of the counter in response to a binary control signal input from the outside. A multivibrator that starts oscillating in response to an input of a clock signal from the outside when in a state and outputs a pulse signal having a frequency higher than that of the clock signal; and a multivibrator when the count number of the counter reaches an arbitrary predetermined number. Means for stopping oscillation of the multivibrator, selecting a pulse signal output from the multivibrator when the control signal is in one state, and selecting an external clock signal when the control signal is in the other state. Means for inputting to the clock terminal of the counter.

〔Example〕

Next, the present invention will be described with reference to the drawings. First
The figure is a block diagram of one embodiment of the present invention. As shown in FIG. 1, the present embodiment includes a test circuit 1 including a selector 2 and a multivibrator 3, and a counter 4 including counters 5 to 8.

In FIG. 1, the selector 2 is switched between a normal input state and a test input state by switching control by a control signal 102. At the time of test input, the clock signal
The multivibrator 3 is operated by 101, and its output signal is supplied to each clock terminal of the counters 5 to 8 included in the counter 4 via the selector 2.

In this case, the multivibrator 3 controls the control signal 10 as shown in FIGS. 2 (a), 2 (b) and 2 (c).
When 2 is high, the first input clock signal 1
Oscillation starts in response to the change from low level to high level of 01, and the pulse signal 103 having a higher frequency than the clock signal
Is output. The output pulse signal of the multivibrator
103 is input to the clock terminals of the counters 5 to 8,
Until the carry signal of each of these counters is output,
An arbitrary number of pulses are continued and counted in the counter 4. In the case of the present embodiment, the counter 4
In the function test, the test can be performed in a short time without dividing the counter 4 and the designed function can be easily confirmed. It is to be noted that, instead of using the carry signal as in the present embodiment, a predetermined decoder is inserted into the output side of the multivibrator 3 and the output of the counter 4 in a short time without dividing the counter 4. It is possible to conduct tests.

In the semiconductor integrated circuit according to the present invention, the control signal 102 is set to the low level and the clock signal 101 is supplied to the counter 4.
, The so-called normal input state, the multivibrator 3 has stopped oscillating. Therefore, there is no change in power consumption at the time of normal input.

〔The invention's effect〕

As described above in detail, according to the present invention, by incorporating a multivibrator in a test circuit of a counter of a semiconductor integrated circuit, the function of the counter can be changed without changing the original performance of the counter during the test of the counter. There is an effect that it can be easily confirmed in a short time.

In addition, there is no change in power consumption when the counter operates at a normal input by a clock signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIGS. 2 (a), (b) and (c) are timing diagrams of main signals in the embodiment, and FIG. 3 is a conventional semiconductor integrated circuit. It is a block diagram of an example of a circuit. In the figure, 1, 14,..., A test circuit, 2,.
...... Multivibrator, 4 ~ 8, 9 ~ 13 ... Counter, 1
5 to 17 ... OR circuit.

Claims (1)

(57) [Claims] 1. A test circuit comprising: a counter; and a test circuit for performing a function test of the counter in response to a binary control signal input from the outside, wherein the test circuit has one of the control signals. A multivibrator that starts oscillating in response to an external clock signal input and outputs a pulse signal having a higher frequency than the clock signal; and a multivibrator when the count number of the counter reaches an arbitrary predetermined number. Means for stopping oscillation; selecting the pulse signal output from the multivibrator when the control signal is in one state; selecting the external clock signal when the control signal is in the other state; Means for inputting to a clock terminal of the semiconductor integrated circuit.