JPS59109934A - digital input circuit - Google Patents

Abstract

PURPOSE:To increase substantially the number of input points by executing a write in an FIFO memory circuit only in case when a state is varied, and reading successively an input information from the FIFO memory circuit by a read signal from a CPU. CONSTITUTION:An information inputted through an external input contact 1 and a filter circuit 2 is led temporarily into a state variation detecting circuit 4, and a detection of a state variation is executed. In case when the state variation is detected, a new information is written in an FIFO memory 6 by a write signal 5. In this state, a central processing circuit 7 can obtain an external information by reading the information in the FIFO memory 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a digital input circuit, and particularly to a scanning type digital input circuit used in a microprocessor application control device.

[Technical background of the invention]

Digital input methods for microprocessor-applied control devices include those using an interrupt method and those using a scanning method, and the present invention relates to the scanning method. The scanning digital input method is often used because it is easy to create software, and a conventional scanning digital input circuit is shown in FIG. Input information from external input contact 1 is passed through filter circuit 2 to buffer dart circuit 3.

The buffer gate circuit 3 opens the dart in response to a read signal from the central processing circuit (CPU) 7 and passes the information to the central processing circuit 7.

[Problems with background technology]

According to the above method, the central processing unit must complete scanning within the minimum operating time of the external input contacts, and cannot read when the number of external input contacts is large.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and relates to a digital input circuit that improves the limit on the number of external input contacts in a scanning type digital input circuit.

[Summary of the invention]

In the present invention, the input information taken in through the external input contact and the filter circuit is once introduced into the state change detection circuit, and only when there is a state change, it is written to the FIFO memory circuit.
This is intended to increase the actual number of input points by sequentially reading input information from the FIFO memory circuit in response to a read signal from the CPU.

[Embodiments of the invention]

It is. The symbols 1.2 and .3 in the figure correspond to those in FIG. The process until the input information from the external input contact 1 passes through the filter circuit 2 is the same as that shown in FIG. However, the information that has passed through the filter circuit 2 is once input to the state change detection circuit 4, and state change detection is performed at regular intervals with the old information in the state change detection circuit 4, where a state change is detected. In this case, new information is written to the PIF'0 memory 6 by the write signal 5. The central processing circuit 7 can obtain external input information by reading the information in the FIFO memory 6.

FIG. 3 is a block diagram of another embodiment of the digital input circuit according to the present invention. Reference numerals 1 to 2 and 4 to 7 in the figure correspond to those in FIG. In this embodiment, an initialization signal 8 from the central processing circuit 7 is added to the FIFO write signal 5 from the state change detection circuit 4. That is, the contents of the FIFO memory 6 can be updated in response to an initialization request from the central processing circuit, and initial data can be reliably read.

〔Effect of the invention〕

As explained above, according to the present invention, since the state change detection circuit and the FIFO memory circuit are added to the scanning type digital circuit and are introduced into the central processing circuit, there is no need to read all information, and the central It is possible to provide a digital input circuit that can lengthen the scanning period of the arithmetic processing circuit and substantially increase the number of digital input processing points.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional scanning type digital input circuit, FIG. 2 is a configuration diagram of one embodiment of the digital input circuit according to the present invention, and FIG. 3 is a diagram showing the configuration of another embodiment of the digital input circuit according to the present invention. be. 1... External input contact 2... Filter circuit 3
... Buffer e-) circuit 4 ... State change detection circuit 5 ... Write signal 6 ... FIFO memory circuit 7 ... CPU 8 ... Initialization request signal (7317) Agent Patent attorney Kensuke Noriyuki (and 1 other person) (5)

Claims (2)

[Claims] (1) In a digital input circuit of a microprocessor applied control device that sequentially inputs input information to a central processing unit by scanning input contacts, the input circuit includes a state change detection circuit for detecting changes in the state of input information. and FIF
Writing to the FIFO memory circuit is performed using a state change detection signal that is performed at regular intervals, and the input information to the central processing unit is input to the FIFO memory circuit.
A digital input circuit characterized by being operated from an IFO memory circuit. (2) The FIF is activated by the initialization signal from the central processing unit.
2. The digital input circuit according to claim 1, wherein the digital input circuit updates the memory contents of the O memory circuit.