JPH0555231U - Printer connection device - Google Patents

Abstract

(57) [Abstract] [Purpose] A branching device is used to automatically select and select a plurality of printers by a switching signal. [Structure] A branching device 1 is connected to a host device via a connecting cable 2, and four signal lines defined as ground lines in the standard Centronics interface standard are connected from the short-circuit prevention circuit 3 of the host device to the connecting cable 2 A power supply line for supplying power to the branching device 1 via the switching device, a switching signal line for transmitting a printer connection switching signal from the host device to the switching connection circuit 1A of the branching device 1, and a host when the printer cable is connected to the branching device 1. A signal from the device is used as a short circuit prevention detection signal line for one forward route and one return route for feeding back from the short circuit prevention signal feedback circuit 1B of the branching device 1, and the host device automatically switches and selects a plurality of printers by a switching signal. Data input / output.
When the printer interface is erroneously directly connected to the host device without passing through the branching device 1, the short circuit prevention detection signal is not fed back to shut off the power supply so that the CPU of the host device is not destroyed. ..

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a printer connection device that enables a host device to control a single printer interface of its own device to automatically print out a plurality of printers.

[0002]

[Prior Art]

 Conventionally, in a computer, only one printer is controlled by one printer interface provided on the computer main body side.

Therefore, when connecting two printers to the computer, it was necessary to connect an external device for controlling the two printers to the printer interface of the computer. In order to switch between the two printers connected to the external device, it was necessary to manually operate the printer changeover switch provided in the external device.

[0004]

[Problems to be solved by the device]

 Normally, in office work using office automation equipment (office automation equipment), for example, in a slip issuing business that requires copying such as purchase orders, a dot impact printer is used to manage the processing contents of those slips. In issuing work, multiple printers are often used for different purposes, such as using a laser printer that does not have a copy function but is high-speed and quiet.

However, in the case where a plurality of printers are properly used in such a manner as described above, as described above, the computer is provided with only one printer interface, and therefore the work of reconnecting the printer connection cable is required. Even if an external device for changing the printer is necessary and the above-mentioned external device is used, the printer can be changed only by the manual operation. As described above, conventionally, when a plurality of printers are switched and used by one computer, manual work is required, which is troublesome and the work efficiency is deteriorated.

As one method for solving this problem, a method in which two or more printer interfaces are provided in a computer and a plurality of printers are switched on the computer side to perform print output can be considered.

However, although recent OA devices have been downsized and connectors have been downsized accordingly, in recent computers that are in the trend of downsizing, there is a need for two or more printers. Securing the space to mount the connector has become difficult.

On the other hand, in the Centronics interface, which is a standard printer interface, its ground line is used as a control signal line for automatic switching of the printer, and signals input from these control signal lines are used as a base. It is conceivable to substitute the power supply line to the external branch device for switching the printer connection with another grounding line of the above Centronics interface, but in this case, the standard Centronics interface for the computer side Centronics interface is used. -If the printer is connected via an interface cable, the power supply line and the ground line on the printer side will be short-circuited and the computer and printer will be damaged.

Then, the printer is connected to one standard printer interface (Centronics interface, etc.) of a host device such as a computer, and among a plurality of connected printers under the control of the host device. If there is a branching device that can automatically switch and connect any printer of the above to the host device, when switching and using multiple printers according to the application, the troublesome work of reconnecting the printer connection cable becomes unnecessary, It is clear that the improvement of printer output work can be realized without hindering the miniaturization of the host device.

An object of the present invention is to connect one standard printer interface (Centronics interface, etc.) of a host device such as a computer, and to control a plurality of connected printers under the control of the host device. It is to realize a branch device that can automatically switch and connect one to the host device.

[0011]

[Means for Solving the Problems]

 The means of this invention are as follows. The branching device 1 (see the block diagram of FIG. 1, the same applies hereinafter) is supplied with power from the host device through a power supply line in the connection cable 2 by a printer interface of the host device and a predetermined connection cable 2. A switching connection circuit for switching and connecting a signal line from the host device to the printer to a signal line for any one of the plurality of printers by a switching signal input from the host device through the connection cable 2. 1A and a short circuit prevention signal feedback circuit 1B that outputs a short circuit prevention signal sent from the host device via the connection cable 2 to the host device via the connection cable 2 as a feedback. The short circuit prevention circuit 3 is provided in the host device, and when connected to the branch device 1 through the connection cable 2, the short circuit prevention signal feedback circuit 1B in the branch device 1 causes the above short circuit through the connection cable 2. Power is supplied to the power supply line to the branching device 1 in the connection cable 2 only when the prevention signal is fed back.

[0012]

[Action]

 The operation of the means of this invention is as follows. When the host device and the branching device 1 are connected via the connection cable 2, the short circuit prevention signal feedback circuit 1B outputs the short circuit prevention signal sent from the short circuit prevention circuit 3 of the host device via the connection cable 2. Is fed back to the short-circuit prevention circuit 3 of the host device via the connection cable 2. In response to this, the short circuit prevention circuit 3 supplies the power output from the power supply circuit in the host device to the branching device 1 via the power supply line of the connection cable 2. As a result, the branching device 1 becomes operable. Then, the branching device 1 connects a signal line from the host device to the printer in the connection cable 2 to a printer among a plurality of printers by a switching signal input from the short circuit prevention circuit 3 of the host device via the connection cable 2. Switch and connect the signal line to one of the printers. On the other hand, when the host device and the printer are connected by the Centronics interface cable without passing through the branching device 1, the above short circuit prevention signal is not fed back to the short circuit prevention circuit 3. Therefore, the short circuit prevention circuit 3 in the host device does not supply power to the connection cable 2. Therefore, even when the host device having the short-circuit prevention circuit 3 is directly connected to the printer by the Centronics interface cable, the power supply line in the host device and the ground line on the printer side are short-circuited and the host device is short-circuited. Or the printer is not destroyed. Therefore, the printer is connected to one standard printer interface (Centronics interface, etc.) of a host device such as a computer, and any printer among a plurality of connected printers is controlled by the host device. It is possible to realize a branching device that can be automatically switched and connected to a host device.

[0013]

【Example】

 An embodiment will be described below with reference to FIGS. FIG. 2 is a block diagram showing the configuration of a system in which two printers A50-1 and B50-2 are connected to a CPU 21 of a computer via a printer cable 30 and a printer branching device 40.

In FIG. 1, a CPU 21 is composed of a microprocessor installed in the host computer main body, a short-circuit prevention control circuit 22 is provided therein, and a Centronics I / C that complies with the Centronics interface standard is provided. An F connector (Centronics interface connector) 26 is provided outside. The Centronics I / F connector 26 of the CPU 21 is provided with a connector 42 of a branching device 40 by a printer cable 30 in which a power supply line 31, a data signal line 32, a switching signal line 33, a short circuit prevention detection signal line 34, etc. are accommodated. -3 is connected.

The data signal line 32 is an 8-bit print data that is defined by the Centronics interface connector standard and that sends the 8-bit print data output by the CPU 21 to the printer A50-1 or the printer B50-2. It consists of data signal line, strobe signal line for handshake, acknowledge signal line, busy signal line, and data signal pair ground line.

The power supply line 31 is a line for supplying power from the CPU 21 of the host computer to the printer A 50-1 or the printer B 50-2 via the branching device 40, and the switching signal line 33 is from the CPU 21 to the branching device 40. A signal line for instructing switching of the printer and a short circuit prevention detection signal line 34 are short circuits output by the short circuit prevention control circuit 22 of the CPU 21 to notify that the printer cable 30 is connected to the branching device 40. It is a signal line for feeding back the prevention detection signal from the branching device 40, which is composed of one forward path and one return path.

All of the above four lines are signal lines defined as ground lines in the Centronics interface connector standard. The branching device 40 has a feedback / branching circuit 41 therein, and the feedback / branching circuit 41 is connected to the Centronics I / F connector 26 of the CPU 21 via the printer cable 30 and the connector 42-3. ing . Further, two standard Centronics I / F connectors 42-1 and 42-2 are externally provided on the branching device 40, and two printers A50- are provided to the two connectors 42-1 and 42-2, respectively. 1 and the printer B50-2 are connected via standard Centronics I / F cables 61A and 61B.

The feedback / branching circuit 41 of the branching device 40 responds to the switching signal sent from the CPU 21 via the switching signal line 33 in the printer cable 30, and outputs the 8-bit print data and the 8-bit print data sent from the CPU 21. The connector that outputs the control signal is switched to either one of the two Centronics I / F connectors 42-1 or 42-2, and those data and control signals are sent to either the printer A 50-1 or the printer B 50-2. Output to one side.

FIG. 3 is a configuration example of the branch circuit unit 410 in the feedback / branch circuit 41. In the figure, a branch circuit unit 410 includes a plurality of signal selection circuits 411T for selectively outputting 8-bit print data and control signals transmitted from the host computer to the printer A50-1 or printer B50-2, and the printer A50-. 1 or a plurality of signal selection circuits 411R for selectively outputting a control signal transmitted by any one of the printers B50-2 to the CPU 21 of the host computer.

The signal selection circuit 411T is provided in a one-to-one correspondence with the plurality of input terminals 423T of the connector 42-3. From the input terminals 423T, the eight data signal lines 32 in the printer cable 30 are provided. In addition, 8-bit print data a1 to a8 output by the CPU 21 and a control signal are input via other control signal lines. Further, one signal selection circuit 411T inputs the 1-bit switching signal c transmitted from the CPU 21 via the switching signal input terminal 412S of the connector 42-3 and the switching signal line 33 of the printer cable 30. Then, each signal selection circuit 411T sends the 8-bit print data a1 to a8 and the handshake control signal transmitted from the CPU 21 according to the logic level of the switching signal c to the Centronics I / F connector. 42-1 output terminals 421T or Centronics I / F connectors 42-2 output terminals 422T via standard Centronics I / F cable 61A or standard Centronics I / F cable 61B. Output to A50-1 or printer B50-2.

[0021] The signal selection circuit 411T is made of three-state buffers d _1, d _2, their three-state buffers d _1, 8-bit print data of data input terminals of d ₂ are both connector 42-3 And a control signal for handshake is connected to the input terminal 423T, and the control signal input terminals are both connected to the switching signal input terminal 423S of the connector 42-3. Also, one output terminal of the three-state buffer d ₁ is connected to the output terminal 421T Centronics I / F connector 42-1 for the printer A50-1, the other output terminal of the three-state buffers d ₂ Is connected to the output terminal 422T of the Centronics I / F connector 42-2 for the printer B50-2.

When the switching signal c input from the switching signal input terminal 423S of the connector 42-3 becomes “L” level, the three-state buffer d ₁ of each signal selection circuit 411T moves from the Centronics I / F connector. The 8-bit print data a _{1 to} a _{8 and the} control signal transmitted from the CPU 21 are output to the output terminals 421T of the output signal 42-1 and the switching signal c becomes the “H” level. The 8-bit print data a _{1 to} a _{8 and the} control signal are output from the three-state buffer d ₂ to each output terminal 422T of the Centronics I / F connector 42-2.

On the other hand, the signal selection circuit 411R is provided in a one-to-one correspondence with the plurality of output terminals 423R of the connector 42-3, and the switching signal input terminal 412S of the connector 42-3 is connected to the printer. The 1-bit switching signal c transmitted from the CPU 21 is input via the switching signal line 33 of the cable 30. Then, each signal selection circuit 411R is connected to the printer A50-1 or the printer B50 via the standard Centronics I / F cable 61A or the standard Centronics I / F cable 61B according to the logic level of the switching signal c. -2, the various control signals input from the -2 are output to the CPU 21 via the respective control signal lines in the printer cable 30.

The signal selection circuit 411R is a three-state buffer d₃, D_FourAnd their three-state buffer d₃, D_FourAre both connected to the output terminal 423R of the connector 42-3, and their control signal input terminals are both connected to the input terminal 423S of the connector 42-3. Also, one of the three-state buffer d₃Is connected to the input terminal 421R of the Centronics I / F connector 42-1 for the printer A50-1, and the other three-state buffer d _Four Is connected to the input terminal 422R of the Centronics I / F connector 42-2 for the printer B50-2.

[0025] When the switching switching signal c inputted from the switching signal input terminal 423S of the connector 42-3 becomes "L" level, printer A50-1 of three-state buffers d ₃ of each signal selection circuit 411R Various control signals input from the input terminal 421R of the Centronics I / F connector 42-1 are output from the output terminals 423 of the connector 42-3, and when the switching signal c becomes the "H" level, the signal selection circuits 411R. Various control signals input from the input terminal 422R of the Centronics I / F connector 42-2 for the printer B50-2 from the three-state buffer d ₄ are output from the output terminals 423 of the connector 42-3.

Next, on the right side of FIG. 4, a configuration example of the feedback unit 440 of the feedback / branching circuit 41 is shown. As shown in the figure, the feedback unit 440 of the feedback / branching circuit 41 is connected to the forward path 34-1 of the short circuit prevention detection signal line 34 transmitted from the short circuit prevention circuit 22 of the CPU 21 of the host computer via the printer cable 30. It has a short circuit prevention detection line 412 for outputting a signal as feedback to the return path 34-2 of the short circuit prevention detection signal line 34. The short circuit prevention detection line 412 transmits a short circuit transmitted from the short circuit prevention circuit 22 inside the CPU 21. The prevention detection signal is fed back to the short circuit prevention control circuit 22 inside the CPU 21.

Further, on the left side of the figure, one configuration example of the short circuit prevention control circuit 22 provided inside the CPU 21 is shown. In the figure, a power supply line 221 for supplying power output from a power circuit (not shown) is provided inside the printer cable 30 for supplying power to the branching device 40 via the switch 223A of the electromagnetic relay 223. Connected to the power supply line 31 of. The coil 223B of the electromagnetic relay 223 has one terminal connected to the power supply line 221, and the other terminal connected to the collector of the NPN bipolar transistor Tr1. When a current is supplied from the power supply line 221 to the coil 223B, the switch 223A is closed, and a current is supplied from the host computer to the branching device 40. The power supply line 221 is also connected to the forward path 34-1 of the short circuit prevention detection signal line 34 of the printer cable 30 via the resistor R1.

The NPN bipolar transistor Tr1 has its emitter grounded, and its base is connected to the pull-down resistor R2 and the return path 34-2 of the short circuit prevention detection signal line 34 of the printer cable 30.

Next, the operation of the embodiment having the above configuration will be described. First, when the CPU 21 of the host computer and the branching device 40 are connected by the printer cable 30, as shown in FIG. 4, the short-circuit prevention control circuit 22 of the CPU 21 of the host computer and the feedback / branching circuit 41 of the branching device 40 are connected. However, they are connected by the power supply line 31 in the printer cable 30, the forward path 34-1 of the short circuit prevention detection signal line 34, the return path 34-2, and a plurality of other signal lines shown in FIG.

With this connection, the short-circuit prevention control circuit 22 supplies the power supplied from the power supply circuit of the host computer via the power supply line 221 to the resistor R 1 and the forward path 34-1 of the short-circuit prevention detection signal line 34. To the feedback unit 440 of the feedback / branching circuit 41 via the. As a result, the feedback unit 440 sends the power source back to the short circuit prevention control circuit 22 via the short circuit prevention detection signal line 34 via the return path 34-2 of the short circuit prevention detection signal line 34.

As a result, the base-emitter of the NPN bipolar transistor Tr1 of the short-circuit prevention control circuit 22 is forward-biased and a current flows through the base, so that the NPN bipolar transistor Tr1 is turned on. As a result, a current flows from the power supply line 221 to the coil 223B of the relay 223, and the generated magnetic force closes the switch 223A, and the power supply line 221 supplies power to the closed switch 223A and the printer cable 30. Power is supplied to the branching device 40 via the line 31.

On the other hand, by mistake, without using the branching device 40, the printer A50-1 or the printer B50-2 is replaced with the standard Centronics I / F cable 61A or the standard Centronics I / F cable 61B shown in FIG. When directly connected to the Centronics I / F connector 26 of the host computer, the power supply line 31, the forward path 34-1 of the short-circuit prevention detection signal line 34, and the return path 34-2 are connected to each other as shown in FIG. All are grounded in the interface circuit on the printer (printer A50-1 or printer B50-2) side.

As a result, the short-circuit prevention control circuit 22 supplies the power from the power supply line 31 via the resistor R1 and the forward path 34-1 of the short-circuit prevention detection signal line 34 to the printer Centronics I / F connector 501A or Centronics I / F. Although it is supplied to the F connector 502B, the power supply is not sent back to the short circuit prevention control circuit 22 because the outward path 34-1 is grounded. Therefore, the NPN bipolar transistor Tr1 remains off, no current flows through the coil 223B of the electromagnetic relay 223, and the switch 223A remains open. Therefore, the current supply line 221 in the short-circuit prevention control circuit 22 and the ground line of the printer A50-1 or the printer B50-2 are not short-circuited. That is, even if the CPU 21 of the host computer and the printer A50-1 or the printer B50-2 are directly connected using the Centronics I / F cable 61A or the Centronics I / F cable 61B, the circuit of the CPU21 of the host computer is destroyed. It will not be done.

Next, the operation after the CPU 21 of the host computer is connected to the printer A 50-1 or the printer B 50-2 via the branching device 40 as described above will be described again with reference to FIG.

The CPU 21 of the host computer sets the switching signal c to the “L” level when performing print output via the printer A 50-1. As a result, as shown in FIG. 3, the "L" level switching signal c is applied to the input terminal 423S of the connector 42-3 in the branching device 40 via the switching signal line 33. As a result, since the control signal input terminals of the three-state buffers d ₁ of the plurality of signal selection circuits 411T in the branch circuit unit 410 are activated, they are input through the plurality of input terminals 423T of the connector 42-3. The 8-bit print data and various control signals transmitted by the CPU 21 can be output from the output terminal 421T of the Centronics I / F connector 42-1 for the printer A50-1.

As a result, the CPU 21 of the host computer outputs the 8-bit print data a _{1 to} a ₈ output to the branching device 40 via the printer cable 30 and various control signals to the standard Centronics I / F cable. Since the data is output to the printer 61A, the host computer can transmit desired 8-bit print data and a control signal for handshake to the printer A50-1.

On the other hand, when the printer A 50-1 detects that the strobe signal output from the CPU 21 is activated via the branching device 40, the printer A 50-1 receives the print data a _{1 to} a ₈ via the branching device 40 and prints it. Output is performed, and after printing is completed, an acknowledge signal is output to the branching device 40. Then, the acknowledge signal is input to the input terminal 421R of the branch circuit unit 410 in the branch device 40 via the Centronics I / F connector 42-1.

As described above, the switching signal c is set to the “L” level via the input terminal 423S to the control signal input terminal of the three-state buffer d ₃ of each signal selection circuit 411R in the branch circuit 410. Since the printer A 50-1 outputs the busy signal output to the input terminal 421R of the Centronics I / F connector 42-1 and the acknowledge signal, etc. from the connector 42-3 output terminal 423R to the host cable via the printer cable 30. It is sent to the CPU 21 of the computer.

As described above, the CPU 21 of the host computer can output desired printout to the printer A 50-1 via the branching device 40. On the other hand, when the printer B50-2 performs print output, the CPU 21 sets the switching signal c to "H" level.

As a result, the 3-state buffer d ₂ of each signal selection circuit 411T in the branch circuit 410 receives the 8-bit print data a ₁ through the input terminal 423T of the connector 42-3. The control signal for a ₈ and handshake can be output from the output terminal 422T of the Centronix I / F connector 422-2.

As a result, the CPU 21 of the host computer can transmit the print data a _{1 to} a ₈ and the control signal for handshake to the printer B 50-2 via the branching device 40.

On the other hand, the printer B50-2, after receiving the strobe signal active from CPU21 through a branching unit 40, when receiving the print data a ₁ ~a _8, it these print data a ₁ ~a ₈ Is printed out, and after printing out, an acknowledge signal is output to the input terminal 422R of the Centronics I / F connector 42-2 in the branching device 40.

As described above, since the switching signal c is applied at the “H” level to the control signal input terminal of the three-state buffer d ₄ of each signal selection circuit 411R in the branch circuit 410, busy signal the printer B50-2 outputs supplied to the input terminal 422 R of the Centronics I / F connector 42-1, acknowledge signals etc., via a three-state buffer d _4, connector 42-3 output terminal It is output from 423 R to the CPU 21 of the host computer.

As described above, the host computer can perform print output using the printer B50-2 while performing handshake control with the printer B50-2 via the branching device 40.

As described above, according to this embodiment, the host computer is connected to the branching device 40 via the printer cable 30, and is defined as a ground wire in the printer cable 30 according to the standard Centronics I / F connector standard. The four signal lines are connected to a power supply line 31 for supplying power from the CPU 21 of the host computer to the branch circuit 40, and a switching signal line 33 for the CPU 21 to instruct the branch device 40 to switch the printer connection. And a short circuit prevention detection signal line 34 composed of a forward path 34-1 and a return path 34-2 for feeding back a short circuit prevention detection signal to the CPU 21 to notify that the printer cable 30 is connected to the branch circuit 40. The Centronics I / F standard connected to the branching device 40 by using the four signal lines The printer A 50-1 and the printer B 50-2 having the connectors 501A and 501B can be automatically switched and selected on the host computer side to perform print output.

In this embodiment, the number of printers connected to the branching device 40 and automatically selectable is two, but the present invention is limited to two. Alternatively, it is possible to automatically switch and select more than one arbitrary plural printers on the host device side such as the host computer.

[0047]

[Effect of the device]

 According to this invention, one standard printer interface (Centronics interface, etc.) of a host device such as a computer is connected, and any one of a plurality of connected printers is controlled by the host device. Since it is possible to realize a branching device that can automatically switch and connect the printers of the above to the host device, when switching and using multiple printers according to the application, the troublesome work of reconnecting the printer connection cable becomes unnecessary. It is possible to improve the printer output work without hindering the miniaturization of the host device.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a diagram illustrating a connection configuration between a host computer and two printers via a printer branching device according to an embodiment.

FIG. 3 is a diagram showing a configuration example of a branch circuit unit in a feedback / branch circuit and this connector.

FIG. 4 is a diagram illustrating a configuration of a short-circuit prevention control circuit of a CPU, a configuration of a feedback unit in a feedback / branching circuit, and a connection method thereof.

FIG. 5 is a diagram for explaining the operation when the short-circuit prevention circuit of the CPU is directly connected to the standard Centronics interface connector of the printer without passing through the branching device.

[Explanation of symbols]

 1 Branching device 1A Switching connection circuit 1B Short circuit prevention signal feedback circuit 2 Connection cable 3 Short circuit prevention circuit

Claims (1)

[Scope of utility model registration request] 1. A printer interface of a host device is connected by a predetermined connection cable, power is supplied from the host device through a power supply line in the connection cable, and input from the host device through the connection cable. A switching connection circuit for switching and connecting a signal line from the host device to the printer in the connection cable to a signal line to any one of a plurality of printers according to the switching signal that is generated, and the connection cable. A short-circuit prevention signal feedback circuit that outputs a short-circuit prevention signal sent from the host device via the connection cable to the host device as a feedback circuit; and a branching device provided in the host device, When the host device is connected to the branching device through the connection cable, A short circuit prevention circuit that supplies power to the power supply line to the branching device in the connection cable only when the short circuit prevention signal is fed back from the short circuit prevention signal feedback circuit via the connection cable. A printer connecting device.