JPH04238518A - Polarity selecting device for rs-422 balanced circuit - Google Patents

Abstract

PURPOSE:To realize the reduction of size, the reduction of weight, and the reduction of cost while improving reliability by reducing the number of signal switching to half in a polarity selecting device for an RS-422 balanced circuit. CONSTITUTION:This device is constituted of a static signal inverting means 31 installed between the RS-422 balanced circuit 21 and an internal circuit 22 and a selecting signal generating means 32 to generate a signal to select the inverting operation of this signal inverting means 31. Since the signal is switched at a transmit/receive data signal side at the opposite side of external equipment 10, the number of switching is small, and a component can be constituted by using a part of terminal equipment as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarity selection device for an RS-422 balanced line.

0002

2. Description of the Related Art Systems comprising a host computer that performs comprehensive data processing and one or more terminal devices connected to the host computer are constructed and used in all industrial fields.

At this time, the host computer side is often configured to be able to output a certain data signal with either +5V or -5V having different polarities, for example, from the viewpoint of data processing convenience and expansion of applicability. Furthermore, it is generally configured so that both data signals with different polarities can be outputted at all times due to cable processing or the like. On the other hand, on the terminal device side, it is desirable to specify the polarity of the transmitted and received signals in terms of device construction. However, if the polarity is fixed for personal convenience in this way, if the polarity is changed to a different one initially or in the medium to long term depending on the usage of the host computer that is an external device, the terminal device There are disadvantages such as lack of applicability and limited usage of the system as a whole. In this way, RS-422 is sent to the terminal equipment side.
A balanced line and a polarity selection device are provided to expand practical applicability to external equipment.

A conventional polarity selection device is generally constructed as shown in FIG. That is, in the figure, received data signals RX・D and C・RX・D(
The polarity is opposite to RX/D, and the same applies hereafter. ) and transmission data signals TX・D and C・TX・D (opposite polarity to TX・D, the same applies hereinafter), a publicly known RS-422 balanced line 21 is provided in the terminal device (for example, a printer) 20. In addition, a mechanical switch (selector switch) is installed between this RS-422 balanced line 21 and the external device 10.
A polarity selection device 30 is provided. This changeover switch (30) is often provided integrally with the terminal device 20.

[0005] Therefore, the changeover switch (30) is
When the selection is switched as shown by the solid line, the signal RX・D becomes +5.
When the signals C, RX, and D are -5V, the internal circuit 22 of the terminal device 20 receives the data signals DX and DATA of +5V. In other words, the external device 10 is connected for reception with signals RX and D having one polarity. Transmission signal TX・
The same applies to D. Here, polarity is unified,
Smooth transmission and reception, the applicability of the entire system, and the degree of freedom in choosing how to use it are expanded.

[0006]

[Problems to be Solved by the Invention] According to this conventional structure, the number of lines (signals RX, D, C, RX) that are twice as many as the transmission signals (DX/DATA, TX/DATA) transmitted and received between the two 10 and 20 is・D, TX・D, C・TX・D)
This goes against the demand for smaller and lighter terminal equipment 20, which requires even a minimum number of cable cores between the two 21 and 30. In addition, if polarity selection is switched at the external multi-core stage of the RS-422 balanced line 21, not only is reliability low with a mechanical switch, but there is also a strong possibility that the characteristic impedance will be affected. ), it is necessary to adopt analog switches with special specifications, which increases the cost burden.

An object of the present invention is to provide a highly reliable and low-cost RS that is compact and lightweight by reducing the number of signal switching by half.
An object of the present invention is to provide a polarity selection device for a -422 balanced line.

[0008]

[Means for Solving the Problems] The present invention provides an RS-422 system for receiving and transmitting a pair of received data having different polarities and a pair of transmitting data having different polarities to and from an external device via an RS-422 balanced line. A balanced line polarity selection device comprising a static signal inversion means connected between the RS-422 balanced line and an internal circuit, and a selection signal for selectively inverting the static signal inversion means. and selection signal generating means for generating.

[0009]

[Operation] In the present invention, the polarity selection device is composed of a static signal inversion means connected between the RS-422 balanced line and the internal circuit, and a selection signal generation means for selectively inverting the signal inversion means. This function selects and switches the minimum number of signals necessary to transmit and receive between the external device and the terminal device, that is, the internal circuit. Therefore, not only is the cable weight and size reduced by halving the number of equal-core wires, but the signal inversion means and selection signal generation means can be integrated into the terminal equipment, and can also be used as a part of the internal circuit, etc., or can be constructed as software, resulting in a significant cost reduction. It is designed to be down and has high reliability.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, this polarity selection device 30 connects an RS-422 balanced line (
It is used for transmitting and receiving via the receiver 21A/driver 21B) 21, and is composed of a stationary signal inverting means 31 and a selection signal generating means 32.

In this embodiment, the static signal inversion means 31 is a two-input Ex-OR gate (exclusive OR) 31A.
, 31B, the output of the receiver 21A and the selection signal SELECT are input to the reception gate 31A,
Depending on the conditions, the received data signal RX/DATA is output to the internal circuit 22. On the other hand, the transmission gate 31B is connected to the driver 21B, and receives the transmission data signal TX/DATA from the internal circuit 22 and the output (RX/DATA) of the gate 31A.
ATA) is input. Therefore, switching is performed by inverting the internal signal (TTL level) of the terminal device 20.

Further, the selection signal generation means 32 is formed by combining the keyboard (not shown), CPU, etc. of the terminal device 21, and outputs a selection signal SELECT by pushing a specific key. ing. However, it may be formed to be generated by data written in a RAM or the like. In this embodiment, the selection signal C SELE
CT (L) uses positive polarity selection (signals RX/D, TX/D)
The selection signal SELECT (H) is used to select the negative polarity (signals C, RX, D, C, TX, D).

Next, the operation will be explained. When selecting positive polarity use with the external device 10, a selection signal C.SELECT (L) is generated from the selection signal generation means 32 and inputted to the signal inversion means 31 (31A). Then, as shown in FIG. 2(a), the gate 31A receives the received signal RX・D input to the receiver 21A and outputs the data signal RX・D.
Outputs ATA to internal circuit 22. On the other hand, the internal circuit 22
A transmission data signal TX/DATA is output from. Since the positive signal RX/DATA is input to one terminal of the gate 31B, the external device 10 is connected from the driver 21B.
Transmission signals TX and D are output to. In other words, selection signal C
・SELECT (L) selects positive electrode use (RX, D, T
You can switch the selection between X and D). On the other hand, selection signal SELEC
By generating T(H), the selection can be switched to negative electrode use (C/RX/D, C/TX/D) as shown in FIG. 2(b).

[0014] According to this embodiment, the stationary signal inversion means 31 and the selection signal generation means 32 are constructed, and the signal switching is performed on the side of the RS-422 balanced line 21 opposite to the external device 10. As a result, the number of signal switching is halved compared to the conventional example, simplifying cable processing, making it smaller and lighter, and reducing costs.

Furthermore, since the signal inversion means 31 is formed from two 2-input Ex-OR gates 31A and 31B, it can be mounted on a printed circuit board for various circuits constituting the terminal device 20, and from this point of view as well, it is simple. It is possible to achieve greater efficiency and lower costs.

Furthermore, since the signal inverting means 31 is of a static type and performs small signal control by inverting the TTL level, it does not adversely affect the characteristics compared to conventional mechanical switch systems, and is lower in cost than analog switches. be. Reliability also increases significantly.

Furthermore, since the selection signal generating means 32 can be constructed by using the constituent elements (CPU, etc.) of the terminal device 20, it is possible to reduce the size and cost from this point as well.

[0018]

[Effects of the Invention] Since the present invention is configured to include a static signal inversion means and a selection signal generation means, and to switch signals between an RS-422 balanced line and an internal circuit, deterioration of characteristics due to impedance changes is avoided. It eliminates the conventional drawbacks of large size and complexity, and is also small, lightweight, low cost, and highly reliable.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation.

FIG. 3 is a circuit diagram showing a conventional polarity selection device.

[Explanation of symbols]

10 External device 20 Terminal device 21 RS-422 balanced line 21A Receiver 21B Driver 22 Internal circuit 31 Stationary signal inversion means 31A, 31B 2-input Ex-OR gate 32 Selection signal generation means

Claims (1)

[Claims] 1. An RS-422 balanced line polarity selection device for receiving and transmitting a pair of received data having different polarities and a pair of transmitting data having different polarities to and from an external device via the RS-422 balanced line. a static signal inversion means connected between the RS-422 balanced line and the internal circuit;
1. A polarity selection device for an RS-422 balanced line, comprising selection signal generation means for generating a selection signal for selectively inverting the static signal inversion means.