JPH07101880B2 - Peripheral device sharing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a peripheral device sharing system for sharing a peripheral device such as a printer with a control device such as a plurality of computers.

[Conventional technology]

FIG. 4 is a block diagram showing a configuration of a system that realizes a conventional peripheral device sharing method. In the figure, reference numerals 1 and 2 are control devices A and B such as microcomputers, and 3 is the control device A1. A printer 4 as a peripheral device shared by B2 is a switch for physically connecting the printer 3 and the control device A1 or the control device B2.

In the figure, a is a Centronics-compliant interface cable (hereinafter referred to as an I / F cable) that connects the control device A1 and the switch 4, and b is a Centronics-compliant interface that connects the control device B2 and the switch 4. I / F cable,
Reference numeral c is a Centronics compliant I / F cable that connects the switch 4 and the printer 3.

Next, the operation will be described.

When the control device A1 uses the printer 3, the switching device 4 physically connects the I / F cable a and the I / F cable c and transfers the print data from the control device A1 to the printer 3. Enables printing.

When the control device B2 uses the printer 3, the switch 4 physically connects the I / F cable b and the I / F cable c, and transfers the print data from the control device B2 to the printer 3. This enables printing.

[Problems to be Solved by the Invention]

Since the conventional system for sharing peripheral devices is configured as described above, a new switching device is required to share the peripheral device, and when an abnormality occurs in this switching device, peripheral devices such as printers are also required. There was a problem such as not being able to control.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a sharing system for peripheral devices that enables sharing of peripheral devices without the switching device.

[Means for Solving the Problems]

The peripheral device sharing method according to the present invention allocates one control line to each control device, and causes each of these control devices to output an occupancy request signal of the usage right as an open collector output when a usage request for the peripheral device occurs. After waiting for a certain period of time, the active signal read from all the control lines is given priority judgment by itself, and the occupation right or abandonment of the right of use is decided.

[Action]

The peripheral device sharing method according to the present invention relates to an active signal read from all the control lines after allowing each control device to output an occupancy request signal for the peripheral device usage right and waiting for a certain time. Since the priority judgment is made by itself, the race condition can be avoided even without the switch.

Example of Invention

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a system that realizes a peripheral device sharing system according to an embodiment of the present invention.
The same or corresponding parts as those of the conventional peripheral device sharing system (FIG. 4) are designated by the same reference numerals and the description thereof will be omitted.

In the figure, 5 is a control line assigned to each of the control devices A1 and B2. In the figure, I / F cables a, b, d
, Which are shown separately, are actually cables that transfer the same control signal.

2 is a block diagram showing the internal configuration of each of the control devices A1 and B2. In FIG. 2, 5a and 5b are the control lines 5.
Is a control line (hereinafter referred to as RA *, RB *) assigned to each of the control devices A1 and B2 that compose the control device. The state of RA * 5a, RB * 5b is the first bit (the least significant bit) of the control device information. Bit) and the second bit (note that the active state is "1" in the following description). 6a and 6b are RA * 5a and RB * 5b
On the other hand, 7 is an inverter that outputs an open collector output of an occupation request signal for each usage right, and 7 is each of the inverters 6a and 6b.
Is a register for holding the information output by the device, 8 is the RA * 5a, R
It is an impact type buffer that reads the status of B * 5b.
For example, if only RA * 5a is active (01)
_{If 2} (binary display) and RA * 5a, RB * 5b are active, information such as (11) ₂ (binary display) is stored. Reference numeral 9 is an internal bus in the control device, 10 is a flip-flop (hereinafter, referred to as F / F, which can be used in the set state and cannot be used in the reset state) for holding information on the use state of the printer 3, and 11 is the printer. A printer I / F for exchanging information with the printer 3.

Next, the operation will be described with reference to the flowchart of FIG. Here, for convenience of explanation, a sharing method for the control devices A1 and B2 (assuming that the control device A1 has a higher priority) will be described, but the number of control devices is not particularly limited.

First, when a request for using the printer 3 is generated in the control device A1 (hereinafter, the same applies to the control device B2), the active information of each RA * 5a, RB * 5b is read from the buffer 8 (step ST1) and each control line Check status (ST
2). If the control line of any one of the control devices is active (in this embodiment, the information (1
0) ₂ and it is considered that the control device B2 is using the printer 3) Forced termination, all control lines are non-active (in this embodiment, RA * 5a is active when RA * 5a is active). If it does not exist, register 01 into (01) ₂
Is set (step ST3), and only RA * 5a is activated by the open collector output of each of the inverters 6a and 6b ((10) for controller B2, ₂ is set and RB * 5b is set.
Wait for a certain period of time (activate only) (step ST
Four). This is because, for example, when requests to use the printer 3 are issued to the control device A1 having a high priority and the control device B2 having a low priority at the same time, both RA * 5a and RB * 5b are non-active in the confirmation in step ST1. The use right occupancy request signal is set in the register 7, but the control device B2 sets (10) ₂ before the control device A1 sets the use right occupancy request signal (01) _2. If step ST5 to be described later is executed, the control device B2 can use the printer 3, and then the control device A1 having a higher priority can also be used (if there are a plurality of usage right occupancy request signals, priority is given. Because the right to use is given to those who have a high degree). In order to avoid such a race condition, it is necessary to wait for all the control devices that have simultaneously issued a use request until the setting of the use right occupancy request signal to the register 7 is completed (until its own control line is activated). is there.

Next, the active information of the buffer 8 is read again (step ST5), and the generation state of the use request is checked (step ST6). In this embodiment, (0
1) ₂ and (10) _{2 in} the case of control device B2 only, and (11) _{2 in} the case of both control devices A1 and B2 (this is control device A1, B2
The open collector output (corresponding to the OR output obtained from (01) ₂ and (10) ₂ ) is used, but in the case of (11) ₂ , each control device that has output the usage right occupation request signal gives priority judgment. (Step ST7), and when it is determined that the priority is low, the register 7 is reset (step ST7).
8) Relinquish the right to use printer 3 by yourself.

On the other hand, the control device A1 having a high priority keeps the contents of the register 7 as it is, and sets the F / F 10 in the set state to make the printer I / F 11 available (step ST9).
After the printing process (step ST10) by the printer 3, the F / F10 is reset, the register 7 is reset (step ST11), and RA * 5a is made inactive.

In the above embodiment, the case where the printer 3 is shared is shown, but other peripheral devices also have the same effect.

〔The invention's effect〕

As described above, according to the present invention, one control line is assigned to each control device, an occupancy request signal for the peripheral device usage right is output as an open collector, and after waiting for a certain time, all control lines are selected. Since it is configured to prioritize the read active signal by itself, it is possible to share peripheral devices with a simple and inexpensive configuration that does not require a switching device, thereby improving system reliability and
It has the effect of improving economic efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a system for realizing a sharing system of peripheral devices according to an embodiment of the present invention, FIG. 2 is a block diagram showing an internal configuration of a control device in the present invention, and FIG. FIG. 4 is a flowchart for explaining a peripheral device sharing system according to an embodiment of the invention, and FIG. 4 is a block diagram showing a configuration of a system for realizing the conventional peripheral device sharing system. In the figure, 1 and 2 are control devices, 3 is a printer, and 5 is a control line. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A method of sharing a peripheral device in which a plurality of control devices share the peripheral device without competing with each other, wherein one control line is allocated to each of the control devices. Output request signal for exclusive use of the right of use to all the control lines,
After waiting for a certain period of time, it reads the signal of the active control line from all control lines and makes a priority decision by itself, and occupies or abandons the usage right of its own control device. Method.