JPH0618381B2 - Data interface circuit - Google Patents

Description

DETAILED DESCRIPTION [Outline] A data terminal device (DTE) such as a printer, a CRT display device, and a processor, and a data line termination device (D) such as a modem.
CE), a standardized cable and connector are provided by providing a switching circuit so that a standardized connection cable can be used for connection, and also by switching the input / output impedance with this switching circuit. It can be connected by using, and can be economical.

[Industrial application field]

The present invention relates to a data interface circuit for connecting to a data terminal device or a data line terminal device.

The data interface circuit has a standardized connection structure, and for example, the Electronic Industries Association (EIA;
Electronic Industries Association) standard RS-2
A configuration conforming to 32C is widely adopted. This RS
-232C is applied to both asynchronous and synchronous serial binary data transmission of full-duplex and half-duplex communication methods with a transmission rate of up to 20 Kb / s. The data terminal equipment (DTE) to which this standard is applied include equipment such as a teleprinter, a CRT display device, a front end port, a processor, and a data line termination device (DC).
E) includes a modem and a home line terminating device (DSU).

As the electrical characteristics of this RS-232C, the input impedance is 3 to 7 KΩ and the output impedance is 300.
+5 when the output voltage Vout is 3 to 7 KΩ or more.
V <Vout <+ 15V, −5V>Vout> −15V. The pin arrangement of the connector is also defined. A 25-pin connector with 13 pins in the upper row and 12 pins in the lower row is used. The male connector is on the data terminal equipment (DTE) side and the female connector is on the data circuit terminating equipment (DCE) side. Used for.

[Conventional technology]

A normal cable and a special cable such as a cross patch cable having a cross connection signal line are selectively used depending on whether the data terminal unit (DTE) or the data circuit terminating device (DCE) is connected to the data interface unit. Met. FIG. 5 is a block diagram of the data communication system, in which 31 and 39 are data terminal devices (D
TE), 32 and 52 are data interface devices (DI
F), 33 and 51 are digital line circuits (DLC),
34 is a network (NW), 35 is an office line trunk (C
BT), 36 is a subscriber circuit (LC), 37 is a public network (C)
ON), 38 and 40 are modems (MDM), 41 to 43 are cables for interfaces such as RS-232C, 4
4, 47 are hybrid circuits (H), 45, 48 are coders (C), and 46, 49 are decoders (D).

The exchange a is composed of the network 34, the office line trunk 35, the subscriber circuit 36, the digital line circuits 33, 51, and the like in the chain double-dashed line, and the subscriber circuit 36, the digital line circuit 51, and the digital face device 52 in the dotted line.
A model control circuit b is configured by the above.

The data terminal devices 31, 39 are connected via the public network 37 and the network 34. In this connection, the public network 37 makes an analog signal exchange connection, and the network 34 makes a digital signal exchange connection. In this case, the data from the data terminal device 31 is subjected to digital-analog conversion and the data terminal device 3
The data from 9 will need to be analog-to-digital converted respectively. Also, between the data terminal device 31 and the data interface device 32, and between the data terminal device 39.
If the cables 41 and 43 between the modem and the modem 38 are the same normal cables, the modem 40 and the modem control circuit b
Cable 42 to and from the data interface device 52 of
Will need to be a special cable that intersects the signal lines.

This is the data interface device 32 or the modem 38.
On the other hand, since the data terminal devices 31 and 39 are connected,
It meets the standard RS-232C interface and is connected using ordinary cables 41 and 43. However, when the modem 40 is connected to the modem control circuit b, the data interface device 52 corresponds to the data terminal device 31, and the connection cable 42 to the modem 40 is
The connection relationship is opposite to that of the modem 38 described above. Therefore, the cable 42 between the data interface device 52 and the modem 40 must use a special cable that crosses signal lines.

For example, as shown in FIG. 6 (a), the driver DR of the data interface device or modem DI and the data terminal device DTE and the receiver RC are correspondingly connected by a normal cable CV. Corresponds to the cables 41 and 43 in FIG. However, as for the cable 42, as shown in FIG. 6 (b), between the data interface device DI and the data circuit terminating device or the modem DCE, both receivers RC and driver DR are ordinary cables. Such a cable CV cannot be used because it will be connected by a CV. Therefore, as shown in FIG. 6 (c), the data interface device DI and the data line terminating device DCE are connected by using the special cable CCV having the signal lines crossed.

[Problems to be solved by the invention]

As described above, it is necessary to identify which device is connected and to select and connect the normal cable or the special cable in which the signal lines are crossed, which is a drawback that the connection work becomes complicated. Further, since the special cable including the connector is relatively expensive, it is not economical to prepare the special cable together with the ordinary cable.

It is an object of the present invention to make it possible to connect various devices with a normal cable only by adding a simple structure.

[Means for solving problems]

Referring to FIG. 1, the data interface circuit of the present invention uses a cable and a connector between the data terminal equipment DTE and the modem or the data interface equipment and between the data interface equipment and the modem in the exchange. In the data interface circuit of the data communication system to be connected, for connecting to the data terminal equipment DTE, or the data circuit terminating equipment DCE such as the data interface equipment in the exchange corresponding to the data terminal equipment DTE. A switching circuit 3 for switching and connecting the receiver 1 and the driver 2 to the terminals A and B of the connector and switching the input / output impedances 4 and 5, and the data terminal device DTE or the data line terminating device D.
A control circuit 6 for controlling the switching circuit 3 depending on which CE is connected is provided.

Then, the data terminal device D
When TE is connected, it is connected by a normal cable shown by a dotted line, and the switching circuit 3 also forms a connection circuit of a dotted line, so that the driver 7 and the receiver 8 of the data terminal device DTE are the receiver 1 and the driver 2, respectively. When connecting the data circuit terminating device DCE, a normal cable shown by a one-dot chain line is connected, and the switching circuit 3 also forms a one-dot chain line connecting circuit, and the receiver 9 and the driver of the data line terminating device DCE are connected. 10 is connected to the driver 2 and the receiver 1, respectively. When the terminal A and the receiver 1 are connected, the impedance 4 is switched to have a predetermined input impedance, and when the terminal A and the driver 2 are connected, for example, the impedance 4 is short-circuited to a predetermined value. Is switched so that the output voltage can be secured. The same applies to the terminal B. The input / output impedance 5 is switched so that a predetermined input impedance is obtained when the receiver 1 is connected and a low output impedance is obtained when the driver 2 is connected. is there.

[Action]

The switching circuit 3 can be constituted by a relatively simple switching element, and the switching circuit 3 is controlled by using only ordinary cables for both the data terminal equipment DTE and the data circuit terminating equipment DCE. By doing so, connection becomes possible. Further, the input / output impedances 4 and 5 are also switched at the same time, whereby the interface standard can be satisfied as a desired input impedance, and a desired output impedance can be determined by using a relatively low power supply voltage. Output voltage can be obtained.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which A and B are terminals, 11 is a receiver, 12 is a driver, 13 and 14 are protection circuits composed of diodes and Zener diodes, and 15 is a control circuit. SW1 to SW6 are switches, S
W is a mode switch, R _{1 to} R ₄ are resistors, + V ₁ ,
-V ₂ is a power supply voltage. The switches SW1 to SW6 and the resistors R ₁ and R ₂ constitute the switching circuit 3 shown in FIG. ₁ , and at the terminals A and B, either the data terminal equipment DTE or the data circuit terminating equipment DCE is a normal cable. Be connected using. The control circuit 15 has a mode changeover switch SW.
The switches SW1 to SW6 are controlled according to the on / off state of the switch to switch the connection between the driver 12 and the terminals A and B, the receiver 11 and the terminals A and B, and the input / output impedance.

The data terminal device DT is connected to the terminals A and B with a cable indicated by a dotted line.
When E is connected, for example, mode switch SW
To turn off. Thereby, the control circuit 15 turns off the switch SW5, turns on the switch SW6, and turns on the switch SW.
1, SW4 is turned on, and switches SW2 and SW3 are turned off. Therefore, the signal from the driver 7 of the data terminal device DTE is applied to the receiver 11 from the terminal A through the resistor R ₁ and the switch SW1. A signal from the driver 12 is applied to the receiver 8 from the terminal B via the resistor R ₃ , the switch SW4 and the switch SW6.

When the data line terminating device DCE is connected to the terminals A and B by the cable shown by the alternate long and short dash line, for example, the mode changeover switch SW is turned on. Thereby, the control circuit 15
Controls the switches SW2, SW3 and SW5 to be turned on and the switches SW1, SW4 and SW6 to be turned off. Therefore, the signal from the driver 10 of the data circuit termination equipment DCE is
It is applied to the receiver 11 from the terminal B via the resistor R ₂ and the switch SW ₂ . The signal from the driver 12 is applied to the receiver 9 from the terminal A via the resistor R ₃ and the switches SW3 and SW5.

As described above, the control circuit 15 controls the mode switch S
Each switch SW1-S according to the ON or OFF input of W
Any structure that controls W6 may be used, so that it can be realized by a relatively simple logic circuit.

The switches SW1 to SW4 can be composed of relatively inexpensive CMOS transistors or the like.
5, SW6 can be constituted by a contact of a relay or a bipolar transistor having a relatively high breakdown voltage. Further, the protection circuits 13 and 14 include switches SW1 to S1.
W4, receiver 11 and driver 12 are connected to the power supply voltage + V
₁ , for protecting against input voltage of -V ₂ or more or noise, Zener diodes are connected in the opposite directions to the ground, and between + V ₁ power supply and -V ₂ power supply. Diodes are connected between them in opposite directions.

The output impedance of the driver 12, since it is intended to substantially determined by the value of resistor R _3, the resistor R ₃ 3
If it is set to 00Ω or more, the above-mentioned RS-232C standard can be satisfied. The input impedance of the receiver 11 is almost determined by the resistors R ₁ , R ₄ or the resistors R ₂ , R ₄ , and the value of R ₁ + R ₄ or R ₂ + R ₄ is
When the standard of RS-232C is satisfied, it is selected to be 3 to 7 KΩ.

Therefore, when the terminal A and the driver 7 are connected, the switch SW5 is controlled to be off, and the input impedance seen from the terminal A becomes R ₁ + R ₄ , and when the terminal A and the receiver 9 are connected, The switch SW5 is controlled to be turned on, the resistor R ₁ is short-circuited, and the output impedance of the driver 12 becomes a value substantially determined by the resistor R ₃ . Similarly, when the terminal B and the driver 10 are connected, the switch SW6 is controlled to be off, and the input impedance seen from the terminal B becomes R ₂ + R ₄ , and when the terminal B and the receiver 8 are connected. , the switch SW6 is controlled to be off, the resistor R ₂ is short-circuited, the output impedance of the driver 12 is substantially determined value by the resistor R _3.

When the protection circuits 13 and 14 operate due to a high input voltage or the like, the input impedance becomes zero, but even in that case, in order to maintain the input impedance of 3 to 7 KΩ, the resistors R ₁ and R ₂ are set. It is necessary to set the resistance to 3 to 7 KΩ, and the resistance values of the resistors R ₁ and R ₂ are selected in relation to the resistor R ₄ . For example, the resistances R ₁ and R ₂ can be set to 3 KΩ, and the resistance R ₄ can be set to 3 KΩ.

Further, when the switches SW5 and SW6 are not provided, the terminal A is connected from the driver 12 via the resistor R ₃ , the switch SW3 and the resistor R _1.
A signal voltage is sent to the resistor R ₁ and the resistance R ₁ is 3 to 7 as described above.
Since it is KΩ and the input impedance of the data line terminating device DCE is also 3 to 7 KΩ, it is applied to the receiver 9 as a signal voltage which is less than about half the output voltage of the driver 12. To increase the signal voltage, it is necessary to increase the power supply voltages + V ₁ and −V ₂ .

However, in the present invention, the input / output impedance is switched by the switches SW5 and SW6.
In the above case, the switch SW5 is turned on and the resistance R ₁
Since output is shorted, the output impedance becomes low. Therefore, it is possible to obtain a desired signal voltage even with a low power supply voltage.

FIG. 3 is a block diagram of the essential parts of another embodiment of the present invention.
The same reference numerals as in FIG. 2 indicate the same parts. This embodiment relates to a case where the configuration of switching between the receiver 11, the driver 12, and the terminals A and B is simplified. The switch SW5 also serves as the switch SW3, and the switch SW6 serves as the switch SW2. The configuration is such that a protection circuit 16 for protecting the driver 12 is added.

Switches SW1 and SW6 are turned on, switches SW2 and SW
When 5 is turned off, the receiver 11 and the terminal A are connected via the resistor R ₁ forming the input impedance, the driver 12 and the terminal B are connected via the resistor R ₃ forming the output impedance, and The connection mode with the terminal device DTE is set.

In addition, the switches SW1 and SW6 are turned off, and the switches SW2 and S are
When W5 is turned on, the receiver 11 and the terminal B are connected via the resistor R ₂ forming the input impedance, the driver 12 and the terminal A are connected via the resistor R ₃ forming the output impedance, and the data Line terminator DC
It becomes the connection mode with E.

Therefore, the input / output impedance is switched together with the switching connection between the receiver 11 and the terminals A and B and between the driver 12 and the terminals A and B.

FIG. 4 is a block diagram of a main part of still another embodiment of the present invention, showing a case where switches SW1 'and SW2' composed of contacts of a relay which does not need a protection circuit, transistors of high withstand voltage and the like are used. The protection circuit 16 is for protecting the driver 12, and the protection circuit 17 is for protecting the receiver 11. The operation is the same as in the case of FIG. 3, and the input / output impedance is switched together with the switching connection between the receiver 11 and the terminals A and B and between the driver 12 and the terminals A and B.

The CMOS transistor has a withstand voltage of about 18 to 20 V and a maximum signal voltage of +15 in the RS-232C standard.
Since it is V to -15V, a protection circuit is required. However, it is relatively inexpensive. On the other hand, the breakdown voltage of the contact of the relay is sufficiently large, and the bipolar transistor can have a breakdown voltage of about 30 V by combining with a diode to prevent breakdown due to reverse voltage between the base and emitter, so protection is possible. No circuit is needed. But,
Relays are difficult to miniaturize and expensive. Further, when a bipolar transistor is used, both positive and negative directions are required, which increases the number of parts and complicates the circuit configuration. From this point of view, the embodiment shown in FIG. 2 has the most economical structure. In addition, a significant cost reduction can be achieved compared to a special cable in which signal lines are crossed.

Although the above-described embodiment shows the configuration according to the standard of RS-232C, it can be similarly applied to other interface standards.

〔The invention's effect〕

As described above, according to the present invention, the control circuit 6 controls the switching circuit 3, and the switching circuit 3 switches and connects the receiver 1 and the driver 2 to the terminals A and B,
In addition, the input / output impedances 4 and 5 are switched. By adding a slight configuration, the data terminal device DTE
It is possible to connect using a normal cable regardless of whether the data line termination device DCE or the data line termination device is connected, and it is not necessary to prepare a special cable in which the signal lines are crossed. Can be down. Further, by switching the input / output impedance, there is an advantage that a desired high signal voltage can be output without increasing the power supply voltage.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIGS. 3 and 4 are main block diagrams of other embodiments of the present invention, and FIG. FIG. 6 is a block diagram of the data communication system, and FIG. 6 is an explanatory diagram of the cable. 1, 8, 9, 11 are receivers, 2, 7, 10, 12 are drivers, 3 are switching circuits, 4 and 5 are input / output impedances, 6 and 15 are control circuits, DTE is a data terminal device, D
CE is a data circuit terminating device, A and B are terminals, and 13 and 1.
4, 16 and 17 are protection circuits, SW1 to SW6 and SW
1 ', SW2' switch, SW is mode _switch, R 1 to R ₄ is a resistor.

Claims (1)

[Claims] 1. A data interface circuit of a data communication system for connecting between a data terminal equipment (DTE) and a modem or a data interface equipment and between a data interface equipment in a switch and a modem by using a cable and a connector. And a terminal of the connector for connecting to the data terminal equipment (DTE) or the data circuit terminating equipment (DCE) such as the data interface equipment in the exchange corresponding to the data terminal equipment (DTE) ( A switching circuit (3) for switching and connecting a receiver (1) and a driver (2) to A) and (B) and switching input / output impedances (4) and (5); and the data terminal device (DTE). Or a control circuit for controlling the switching circuit (3) depending on which of the data circuit terminating equipment (DCE) is connected Data interface circuit, characterized in that it comprises a 6) and.