JPH03118652A - Integrated circuit - Google Patents

Abstract

PURPOSE:To selectively use a 1st control signal received from an interface circuit or a 2nd control signal received directly from outside as an effective control signal by setting one of both control signals at a prescribed level. CONSTITUTION:A control signal A is inputted via a serial bus interface circuit 11 and a control signal D is inputted directly from outside. When the signal A is selected and used by an integrated circuit IC, an external pin 14 is earthed. Thus the signal A held by a serial bus register 12 is sent directly to a serial bus from an OR gate 13. When the signal D is selected, the pin 14 is connected to another IC and a reset signal C is inputted to the register 12. Then the contents of the register 12 are initialized and the signal D inputted via the pin 14 is directly outputted via the gate 13.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to integrated circuits such as LSIs.

(Prior Art) Conventionally, as shown in FIG.
The multiplexer 4 is used to select whether to operate based on the control signal A input through the serial bus interface circuit 2 and the serial bus register 3, or based on the control signal B input directly from the outside. was. Which control signal to select in the multiplexer 4 is determined based on a selection signal input via an external pin 5.

However, dedicating one of the external pins to the selection signal input to the multiplexer 4 described above is a factor that hinders functional expansion in integrated circuits with a limited number of package bins. This could not be said to be the preferred method as it could lead to this. Furthermore, the configuration of the multiplexer 4 requires a large number of gates, resulting in a problem of high cost.

(Problem to be solved by the invention) In this way, in conventional integrated circuits, one external pin is occupied for selecting control signals, and this is one of the factors that prevents expansion of functions. It had become. Also,
There is also the problem of high cost because it requires a large number of gates.

The present invention is intended to solve these problems, without using external pins, and with a smaller number of gates.
The object of the present invention is to provide an integrated circuit that can select either a control signal input through an interface circuit or a control signal input directly from the outside as a valid control signal.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the integrated circuit of the present invention includes a first control signal input means for inputting a control signal through an interface circuit, and a control signal input means for inputting a control signal from the outside. and a gate that performs a predetermined logical operation from the control signals inputted from the first and second control signal input means, respectively. By setting one control signal to a predetermined level, the other control signal is output from the gate as an effective control signal.

(Function) In the integrated circuit of the present invention, a gate is provided that performs a predetermined logical operation from each control signal inputted from the first and second control signal input means, and one of the control signals is input to a predetermined value. level. As a result, the other control signal is outputted from the gate as a control signal valid for the integrated circuit.

Therefore, according to the present invention, either a control signal input through an interface circuit or a control signal input directly from the outside can be converted into an effective control signal without using external pins and with a smaller number of gates. It is possible to select as.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram for explaining the configuration of a control signal input system in an integrated circuit according to an embodiment of the present invention.

In the figure, 11 is a serial bus interface circuit that controls signal input to an integrated circuit such as an LSI;
is a serial bus register that latches the control signal A received by the serial bus interface circuit 11 in accordance with the data latch clock B and temporarily holds it. Note that the contents of this serial bus register 12 are initialized by inputting a reset signal C. In addition, 13 takes the logical sum of the control signal A held in the serial bus register 12 and the control signal input directly from the outside via the external pin 14, and uses the result as an effective control signal in the integrated circuit. This is an OR gate for outputting to the serial bus.

In an integrated circuit having such a configuration, when selecting the former between the control signal A input through the serial bus interface circuit Th1l and the control signal input directly from the outside and using it in the integrated circuit, the external pin 1
Connect 4 to ground.

As a result, the control signal A held in the serial bus register 12 is directly sent from the OR gate 13 to the serial bus.

When selecting a control signal input directly from the outside, connect the external pin 14 to another integrated circuit (not shown) and input the reset signal C to the serial bus register 12.

As a result, the contents of the serial bus register 12 are made clear, and the control signal input via the external pin 14 is
It is output from the OR gate 13 as it is.

Thus, according to the integrated circuit of this embodiment, either the control signal A input through the serial bus interface circuit 11 or the control signal input directly from the outside can be converted into a valid control signal without using an external pin. It is possible to select as.

Moreover, the integrated circuit of this embodiment is a simple logic gate (O
Since the configuration uses the R gate 13), the number of gates is considerably smaller than that of an integrated circuit using a conventional multiplexer, and as a result, costs can be reduced.

[Effects of the Invention] As explained above, according to the integrated circuit of the present invention, a control signal input through an interface circuit and a control signal input directly from the outside can be processed without using external pins and with a smaller number of gates. It becomes possible to select either one of them as an effective control signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining the configuration of a control signal input system in an integrated circuit according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a control signal input system of a conventional integrated circuit. 11... Serial bus interface circuit, 12...
・Serial bus register, 13...OR gate.

Claims (1)

[Claims] A first device that inputs a control signal through an interface circuit.
a second control signal input means for directly inputting a control signal from the outside; and a gate for performing a predetermined logical operation from the control signals input from the first and second control signal input means, respectively. An integrated circuit comprising the following: By setting one of the control signals to a predetermined level, the other control signal is output from the gate as an effective control signal.