JPH04305749A - Rs232c interface circuit - Google Patents

Abstract

PURPOSE:To improve the necessity of manual switching of a pair of signal lines in an RS232C connector at the time of mutually connecting respective data terminal equipments(DTEs) and at the time of connecting the DTE to a data circuit terminal equipment (DCE). CONSTITUTION:A signal judging circuit judges the existence of a signal outputted from the RS232C connector 3 to an external device and whether an opposite side receiver is connected (low impedance) or unconnected (high impedance) when there is no signal and automatically keeps the connection between the connector 3 and the self-device or switches respective signal lines in a pair.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an interface circuit that automatically and correctly switches the connection between a connector conforming to RS232C as a standard serial interface standard for connecting a computer terminal device and the own device according to the other device. The present invention relates to an RS232C interface circuit. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

0002

2. Description of the Related Art FIG. 4 shows a DCE (data line terminal equipment) 1-2 and a DTE (RS232C connector 3-1 with a data terminal equipment 1-1) each equipped with a connector compliant with RS232C (referred to as an RS232C connector for convenience). 3
Figure 5 shows how to connect two DTEs.
A method of connecting the same connector 3-1 between 1-1 is shown. That is, the RS232C connectors 3-1 and 3-2 respectively have a data terminal ready line (terminal) ER, a data set ready line (terminal) DR, a transmission request line (terminal) RS, and a transmission ready line (terminal).
It has CS, sending data line (terminal) SD, receiving data line (terminal) RD, and signal grounding line (terminal) SG, but D
Since CE1-2 is a device that terminates the data line, RS232 connects these two connectors 3-1 and 3-2.
In the C cable 5, the above-mentioned terminals having the same symbols may be connected one to one (straight). But two DTE1−
In the connection between two DTEs, as shown in Figure 5, the data terminal ready line ER of one DTE 1-1 becomes the data set ready line DR to the other DTE 1-1, and similarly, the transmission request line RS of one DTE becomes the data set ready line DR to the other DTE 1-1. is the transmittable line CS, and the transmitting data line SD of one DTE becomes the receiving data line RD of the other DTE, so the cable 5 that connects the two DTEs is a pair of signal lines ( ER and DR
, RS and CS, SD and RD) must be crossed and connected.

0003

[Problem to be solved by the invention] In this way, RS232
Conventionally, the C interface circuit has a problem in that it cannot be connected until it has been confirmed whether the other device to be connected is the DTE 1-1 or the DCE 1-2. To solve this problem, cables have been proposed in which a manual switch is installed on the RS-232C cable 5 to manually switch between cross connection and straight connection, but in the end it is necessary to check whether the other party itself is DCE or DTE. In addition, there is the inconvenience of having to switch manually. Therefore, this invention
For RS-232C, the signal and control lines on the RS-232C connector of the own device are automatically connected to match the connection of the other device by circuit operation, eliminating the need for manual operations when connecting devices. The objective is to provide an interface circuit.

0004

[Means for Solving the Problems] In order to solve the above problems, an interface circuit according to claim 1 is provided between a connector (such as 3) conforming to RS232C as a standard serial interface standard and the own device. The interface circuit includes input signal detection means (signal determination circuit 1
1, etc.), the connector and the own device are normally connected so that the connector is a normal RS232C compliant connector of the own device, and the external side detected by the input signal detection means is When an input signal is to be input to a signal line for signal output from the own device, connect the signal lines that are paired with each other among the signal lines on the connector from the own device to the connector. (logic circuit 13, switch circuit 14, etc.), and

In the interface circuit according to claim 2, in the interface circuit according to claim 1, the input signal detection means adjusts the predetermined power supply voltage to a predetermined level in a state where the connection between the connector and the own device is disconnected. A resistor voltage divider circuit (resistance R1) with a predetermined input impedance that divides the voltage into
, R2, etc.) and the relevant signal line, and then set the voltage level of this signal line to a predetermined reference voltage (V0, V1, etc.).
The presence or absence of the input signal is determined by comparing the input signal with the input signal.

[0006]

[Operation] The signal voltage on the RS-232C signal line is
When the other device is connected, if it is an input signal to the other device, the input impedance should be 3KΩ to 7KΩ according to the regulations.
KΩ and close to 0V, and if it is an output signal from the other device, it must be in the mark signal state, that is, -3V to -15V.On the other hand, if the other device is not connected,
This focuses on the fact that the signal line is in a high impedance state with respect to the signal ground line SG, and in short, the signal line is 0.
The signal is judged by a signal judgment circuit that judges whether it is close to V, -3V to -15V, or high impedance, and based on the judgment result, the RS-232C signal line on the own device side and the other party's This is intended to automatically connect cable side signal lines correctly.

[0007]

Embodiments An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a block diagram showing the main configuration of an embodiment of the present invention. In the same figure, 10 is RS23
2C interface circuit, 1A is the own device, and 1B is the other device. 3 (3A, 3B) is a connector for RS232C, 3A is a connector belonging to this interface circuit 10, and 3B is connected to the connector 3A for RS232C.
This is a connector that is connected to the counterpart device 1B via a cable 5. FIG. 1 shows a circuit for only one pair of signal lines a and b as described above. This pair of signals (lines) corresponds to SD and RD, for example, and the other signal pair ER
Circuits similar to those in FIG. 1 also exist for DR, RS, and CS.

Also, in FIG. 1, 11 (11a, 11b)
are signal determination circuits having the same configuration, and 21a and 21b are signal determination outputs as the determination results of these 11a and 11b, respectively. 13 is a logic circuit that outputs the judgment outputs 21a and 2
1b, outputs the signal 22, and switches the switch circuit 14.
control switching. Depending on the switching of this switch 14, the signal lines a and b are connected straight to the signal lines f and g, respectively, or the signal lines a and b are connected straight to the signal lines g and f, respectively.
may be cross-connected. Note that here f is the own device 1A
The signal line g on the input side is also the signal line on the output side from the own device 1A.

FIG. 2 shows an embodiment of the configuration of the signal determination circuit 11 shown in FIG. In FIG. 2, DRV happens to be the signal line a
R in the other device 1B when it is assumed that it is connected to
The S232C output driver, RCV, is the RS232C output driver, assuming that it also happens to be connected to signal line b.
It is a receiver. Note that in some cases, neither the output driver DRV nor the receiver RCV exists on the other side, and the signal lines a and b
may be in an open (no connection) state. Note that before this signal judgment circuit 11 outputs the judgment output 21 (21a, 21b), as will be described later, the signal lines f, g, etc. of the own device 1A and the connector 3A (therefore, the switch circuit 14)
It is assumed that the connection with the signal determination circuit 11 is disconnected, and the device 1A is configured so as not to affect the determination by the signal determination circuit 11.

In this signal determination circuit 11, voltage levels obtained by dividing the voltage of a power supply (not shown) by resistors R1 and R2 are connected to signal lines a and b, respectively. However, this signal line impedance (therefore the values of resistors R1 and R2) is
B's RS232C driver DRV and receiver RC
Make sure that the impedance is sufficiently higher than V.

Assuming that the signal line a is connected to the output signal of the partner device 1B (that is, the output driver DRV) as shown in FIG. 2, the output voltage is maintained at the mark signal voltage level of -3V to -15V. ing. Also, assuming that signal line b is connected to receiver RCV of partner device 1B, signal line b has an input impedance (3KΩ to 7KΩ) lower than the impedance of resistors R1 and R2, and 0V
maintained at the level. Furthermore, when the signal lines a and b are disconnected, the impedance to the signal ground line SG when looking at the other device 1B from the signal lines a and b is high impedance, so the signal lines a and b are connected to the resistor R1, The signal level is maintained by the divided voltage determined by R2.

Reference numeral 15 denotes a comparison circuit which inputs the comparison reference voltages V0, V1, V2 of the three voltage levels mentioned above, and this comparison circuit 15 inputs the reference voltages V0, V1, V2 and the voltages of the signal lines a, b. By comparison with
, the signal determination outputs 21 (21a, 21b) are output as the three determination results of whether it is connected to the receiver RCV (referred to as input determination) or not connected (referred to as non-connection determination).

FIG. 3 shows an embodiment of the detailed configuration of the logic circuit 13 and switch circuit 14 portions of FIG. 1. Note that the circuit in FIG. 3 is described using active "H" logic. In FIG. 3, the signal judgment outputs 21a and 21b in FIG.
3, but if the signal determination output 21a is input determination and the signal determination output 21b is output determination, AND gate 31 outputs "H" output 22-1, and relay driver 41 of switch circuit 14 Turn on relay X1 via . At the same time, the OR gate 33 of the logic circuit 13 is also “H”.
" output 22-3 and turns on relay X3 via relay driver 43 of switch circuit 14. As a result, contact X1a of relay X1 is turned on, and contact X of relay X3 is turned on.
3a turns on. As a result, the signal line a on the partner device 1B side
and the signal line g on the side of the own device 1A are connected, and the signal line b on the side of the other device 1B and the signal line f on the side of the own device 1A are connected, resulting in the above-mentioned cross connection.

Conversely, when the signal judgment output 21a is for output judgment and the signal judgment output 21b is for input judgment, A of the logic circuit 13
ND gate 32 and OR gate 33 output "H" outputs 22-2 and 22-3, respectively. This turns on relays X2 and X3 via relay drivers 42 and 43, respectively, and thus turns on relay contacts X2a and X3a. As a result, signal lines a and f are connected, and signal lines b and g are connected, resulting in the above-mentioned straight connection. Further, when the signal determination outputs 21a and 21b determine that there is no connection, the circuit in FIG. 3 does not change. The above embodiment is an example of a basic logical configuration, and it is also possible to combine the output judgment logic of the judgment result to further improve the reliability of automatic connection.

[0015]

[Effects of the Invention] According to the present invention, the connector 3 conforms to RS232C as a standard serial interface standard.
An interface circuit provided between the connector 3 and the own device 1A includes at least a signal determination circuit 11 that detects the presence or absence of an input signal on each signal line from the other device 1B to the connector 3, and a signal judgment circuit 11 that detects the presence or absence of an input signal on each signal line from the other device 1B to the connector 3, and a signal judgment circuit 11 that normally connects the connector 3 to the own device. The connector 3 and the own device 1A are connected so that the connector 3 is a normal RS232C compliant connector of the own device 1A, and the input signal from the other device 1B detected by the signal determination circuit 11 is transmitted from the own device 1A. When the signal is to be input to the signal line for signal output on the connector, the connection of the pair of signal lines of each signal line on the connector from the own device to the connector is mutually switched. logic circuit 1
3. Since it is equipped with a switch circuit 14, it is no longer necessary to check whether the device is DTE or DCE or manually rearrange the connector pins for inter-device signals when connecting the connector. is no longer needed. Also, depending on the device, if the partner device does not have a control line function (
In other words, in the above-mentioned case of no connection), the output signal from the own device side may be folded back to the paired signal, but in this case as well, a control signal is input from the own device side to the logic circuit 13 of the present invention,
Moreover, if a return switch section is added to the switch circuit 14, automatic connection of the return signal becomes possible easily.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main configuration of an embodiment of the present invention.

[Figure 2] Detailed configuration diagram of the signal determination circuit also shown in Figure 1

[Figure 3
】Detailed configuration diagram of the logic circuit and switch circuit in Figure 1 as well.

[Figure 4] Diagram showing an example of a connection between a data circuit terminating equipment (DCE) and a data terminal equipment (DTE)

[Figure 5] Diagram showing an example of connections between data terminal equipment (DTE)

[Explanation of symbols]

1A Own device 1B Other device 3 (3A, 3B) RS232C connector 5
RS232C cable 10 Interface circuit 11 (11a, 11b) Signal judgment circuit 13
Logic circuit 14 Switch circuits a, b Paired signal lines f, g on the other device's side Signal lines 21a, 21b on the own device's side as a pair Signal judgment output 22 Logic circuit output

Claims (2)

[Claims] 1. An interface circuit provided between a connector conforming to RS232C as a standard serial interface standard and the own device, the interface circuit detecting the presence or absence of an input signal on each signal line from the outside to the connector at least. an input signal detecting means, and an external side detected by the input signal detecting means, which connects the connector and the own device so that the connector is normally a normal RS232C compliant connector of the own device; When an input signal from the self-device is to be input to the signal line for signal output from the self-device, the input signal from the self-device to the connector of each pair of signal lines on the connector is 1. An RS232C interface circuit characterized by comprising means for mutually exchanging connections. 2. The interface circuit according to claim 1, wherein the input signal detection means detects a predetermined input that divides a predetermined power supply voltage to a predetermined level in a state where the connection between the connector and the own device is disconnected. The RS232 is characterized in that an impedance resistance voltage divider circuit and the relevant signal line are connected, and the voltage level of this signal line is compared with a predetermined reference voltage to determine the presence or absence of the input signal.
C interface circuit.