JP2525185B2 - Interface circuit - Google Patents

Description

The present invention relates to an interface circuit.

[Conventional technology]

In the conventional technique, in the interface circuit in the circuit A for connecting the circuit A and the circuit B, the output signal line on the circuit B side shows an OFF signal when not in operation and a signal line which is ON signal when operating. , When the circuit A and the circuit B are connected, the circuit B in the interface circuit in the circuit A
According to the side signal, when not connected (that is, when the input is open), it is generally assumed that the OFF signal is input and receives the OFF signal (attach a pull-down resistor to the input terminal). ． And while receiving the OFF signal, the circuit A
It is general that the processing inside is stopped and cannot be continued or started. [Problems to be Solved by the Invention] Consider a case where a terminal is considered as an object equivalent to the circuit A and a modem is considered as an object equivalent to the circuit B. There are many modems that have almost the same functions,
In many cases, they use an RS-232C interface circuit, but depending on the model of the modem, it is used.
The RS-232C control signal lines are different, and the control signal lines required for a certain terminal may not always be output. Even if the required control signal line is output, the OFF signal is output at a timing at which processing cannot continue unless the processing timing is matched and the terminal does not output the ON signal. Some modems do. Although such a modem has almost the same processing sequence and almost the same function as the recommended modem of the terminal, it cannot be used for the terminal due to a defect of some control signal lines. There is a problem that is. [Means for Solving Problems] An interface circuit according to the present invention is an interface circuit provided in a first circuit for connecting a second circuit to a first circuit, wherein the second circuit is A plurality of output signal lines that output an OFF signal during operation and output an ON signal during operation are provided, and a predetermined output signal of the second circuit to be connected to a predetermined input signal line of the first circuit. Signal conversion means for generating an ON signal when there is no line, and for generating a signal according to the output signal from the second circuit when the predetermined input signal line and the predetermined output signal line are connected, Switch means arranged before the signal conversion means for blocking or passing an output signal from the second circuit.

〔Example〕

Examples of the present invention will be described below. FIG. 1 shows an example of connection between a device A (terminal) including the interface circuit of the present invention and another device B (modem).
0 is a device A (terminal) 11 is a device B (modem), 12 is an interface circuit for connecting the devices A and B, and a connector 13 for connecting a connection cable 15 for connecting B have. Similarly, there is a connector 14 on the B side as well.
By connecting A and B in this way, mutual signal conversion can be performed. The function of the interface circuit is to send and receive appropriate signals. Figure 2 shows the interface circuit in A of Figure 1 with RS
This is an example of a -232C interface circuit, and the figure is a part of it. 20 corresponds to the connector 13 in FIG. 1, 21 to 23 are output signal lines from this interface circuit to external equipment, and 24 to 26.
Shows the input signal lines from the external equipment. The input signal lines 24 to 26 are input to the signal processing unit 50 through the signal conversion units 33 to 35 and the signal lines 44 to 45, respectively. On the other hand, the output lines 40 to 42 of the signal processing unit of 50 become the signal lines of 21 to 23 via the signal converting units 30 to 32 and become the output signal lines to the outside.The output of 21 to 23 in the case of the RS-232C interface circuit As signal lines, send data line (SD), send request (RS), terminal ready (E
R) etc., and the input signal lines of 24 to 26 include reception data (RD), transmission request (CS), reception carrier detection (CD), etc. The signal conversion unit of 30 to 32 processes 50 signals. When the output logic of the part is ON, it becomes + Vrs, and when it is OFF, it becomes −Vrs (however, 5V ≦ Vrs ≦ 15V). On the other hand, the signal converters 33 to 35 are
If the partner device (B (modem) in Fig. 1) connected to the ~ 26 signal line outputs + Vrs, 50
Outputs a signal that turns ON the input logic of the signal processing part of the signal in response to the input when -Vrs is output, and turns it ON when the input is electrically open. It has a function to output a signal. With such a circuit configuration, even when the specific control line is not output from the partner device (modem),
In the interface circuit on the terminal side, the corresponding signal becomes an open input and an ON signal is received. As a result, OF
When the F signal is received, even if the terminal side processing sequence is such that the processing is interrupted or stopped, the control line does not receive the OFF signal, so the processing can be started and continued. FIG. 3 is a more specific embodiment of the signal conversion units 34 and 35 in FIG. 2. References 34 and 35 are 60, 26 input lines are 63.45 and output lines are 65. 63 The input line of is passed through the input line control unit of 62 and is input to the signal conversion unit of 61. The function of the input line control unit of 62 is to switch the input signal line and transmit the input signal to 61 as it is. It is a switch to switch on or off, and many methods such as instrumental means and electrical means are conceivable, and the switching direction can be easily selected. In the circuit of 61, the input 63 is connected to 76 by the resistance of 72.
It is connected to the inverter of (the input threshold is Vcc / 2). The diode of 71 is connected between the 76 input of 77 and the ground of 70, and 74 is connected between the power supply of 75 and Vcc. The diode of 73 and the resistor of 73 are connected.The function of the signal conversion unit of 61 is that when the input level of 63 is + Vrs, the signal that turns on the logic of 65 (GND level in this case) If it is −Vrs, the logic signal is OFF (in this case, Vcc level (=
5V)) according to the input, and is ON when the input is electrically open (GN in this case).
D level) output function (65 in this embodiment)
The logic of is negative logic). To be more specific, when 63 inputs are open and 62 inputs are open.
When signal cutoff is selected in the input line control section of
The electrical level of 73 has a pull-up resistance of 73 (Vcc
-(74 diode drop voltage)) and the output of 77 is
It becomes GND level (ON). In the conventional technology, there is no pull-up resistor for 73, and there is a pull-down resistor between 70 and GND.
When the input was open, the output of 77 was at Vcc level (OFF). On the other hand, when the switching unit of 62 is selected to be connected, when 63 is + Vrs, 76 also becomes + Vrs, the output of 77 becomes GND level (ON), and the input of 63 is −Vrs,
Since current flows through the resistors from 70 to 72, 76 becomes GND level and 77 output becomes Vcc level (OFF). The above functions are realized. Fig. 4 is a diagram for explaining the consideration when the terminal A (50) incorporating the interface circuit of Fig. 2 and the modems B1, B2, B3 of 51, 52, 53 are connected. It is a modem that has an RS-232C connector and has a built-in RS-232C-compliant interface circuit and can perform almost the same processing. B1 is the recommended modem for terminal A of 50, and the cable of 54 is
Normal operation is possible when connected to the 55 connector.
On the other hand, the modems B2 and B3 of 52 and 53 are not outputting some of the control lines output from the connector of 55,
The processing sequence is slightly different from that of the B1 modem, and some of the control lines temporarily output the OFF signal at the timing when the B1 should have been outputting the ON signal, or the OFF signal is output. Since it is a modem having a processing sequence that continues, it is a modem that operates abnormally such that processing is interrupted or stopped without the interface circuit according to the present invention. Even in such a modem, by using the interface circuit according to the present invention on the terminal side, the external signal is cut off by the input line control unit 62 in FIG. 3 at a temporary certain timing or in a certain state. Or, when using a specific modem, by constantly shutting off and using it, the terminal side recognizes that the corresponding control line is ON, so the terminal side can continue and start processing etc. , B2,
As the B3 modem can be used, the B2 and B3 modems can be used.

As an example of the present invention, a terminal and a modem are taken as an example.
Although the RS-232C interface has been described, it goes without saying that the present invention can be applied to various interfaces.

〔The invention's effect〕

As described in detail above, according to the interface circuit of the present invention, the control signal of the second circuit may not be output, or the output control signal of the second circuit may interrupt the processing of the first circuit. Even with the control signal for stopping, there is an effect that the abnormal operation of the first circuit can be prevented. Further, there is an effect that the connection cable for connecting the first circuit and the second circuit may be common to the plurality of second circuits.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the present invention. FIG. 2 is a block diagram of the RS-232C interface circuit in A of FIG. FIG. 3 is a circuit diagram showing a more specific example of the signal conversion units 34 and 35 in FIG. FIG. 4 is a diagram for explaining consideration when connecting the terminal A (50) incorporating the interface circuit of FIG. 2 to the modem. 10 …… Device A (terminal etc.) 11 …… Device B (modem etc.) 34,35 …… Signal converter 61 …… Signal converter 62 …… Input line controller

Claims (1)

(57) [Claims] 1. An interface circuit provided in a first circuit for connecting a second circuit to a first circuit, wherein the second circuit outputs an OFF signal when not operating and an ON signal when operating. When a plurality of output signal lines for outputting are provided, and the predetermined output signal line of the second circuit to be connected to the predetermined input signal line of the first circuit does not exist,
A signal conversion unit that generates an ON signal and generates a signal according to the output signal from the second circuit when the predetermined input signal line and the predetermined output signal line are connected; An interface circuit which is provided and which switches means for blocking or passing the output signal from the second circuit.