JPH076108A - Communication equipment for display device - Google Patents

Abstract

PURPOSE:To shorten communication time between a ring adaptor and a programmable controller and to improve the degree of freedom in the display of a display device. CONSTITUTION:Plural display devices D1 to Dk connected to a private line 35 are operated based upon information stored in the programmable controller 31. The ring adaptor 32 is intervened between a ring unit 33 in the controller 31 and the line 35. The adaptor 32 acquires display picture numbers indicating pictures to be displayed on the display devices D1 to Dk from the controller 31, and then acquires all information required for displaying the pictures of the acquired display screen numbers from the controller 31. The information is distributed into the display devices D1 to Dk. Thereby the quantity of information to be simultaneously read out from the controller 31 by the adaptor 32 can be extremely reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to data communication between a display device for displaying an operating state or an abnormal state of a production line and a host device such as a programmable controller connected to the display device. The present invention relates to an applied communication device for a display device.

[0002]

2. Description of the Related Art Machine tools and the like installed on a production line are controlled by, for example, a programmable controller and are automatically operated. In such cases,
2. Description of the Related Art Conventionally, a display device including a liquid crystal display panel or the like has been used to display the operation status of a production line or to notify an abnormality that has occurred in the line. The display device acquires the necessary information from the programmable controller,
The display corresponding to the acquired information is performed. A plurality of display devices may be connected to one programmable controller, and in such a case, different information is generally displayed on the plurality of display devices.

Conventionally, two types of methods have been adopted for data communication between a display device and a host device such as a programmable controller. The first method is a method in which a host device executes a program for communication to give necessary information to a display device to passively operate the display device. The second method is a method in which the display device actively acquires the necessary information by reading the contents of the memory or the like in the host device. This second method is called a programless method because it is not necessary to install a communication program in the host device.

When performing data communication between the programmable controller and the display device by the programless method, a communication unit called a link unit is mounted on the programmable controller side. The link unit and the display device are interconnected by a communication cable. The main function of the link unit is to receive the request from the display device, read the contents of the memory or the like included in the programmable controller, and send the contents to the communication cable.

However, in general, the link unit has one
Only one display device can be connected. for that reason,
When connecting two or more display devices to one programmable controller, a plurality of display devices are connected to the programmable controller without using the link unit. In this case, since the data communication is performed by the first method instead of the programless method, it is unavoidable to incorporate a complicated communication program in the programmable controller.

What has been devised there is a prior art in which an adapter is interposed between the link unit and the display device, and the conceptual configuration thereof is shown in FIG. The programmable controller 5 is provided with a link unit 6, and an adapter 10 is connected to the link unit 6. The adapter 10 includes a plurality of indicators 2
, 2N (hereinafter, referred to as "display unit 2" when collectively referred to) as a plurality of adapters 11, 12, ... 1N (hereinafter referred to as "adapter" when collectively referred to as "adapter 2"). 1 ”) is connected through the dedicated line 8.

Each display unit 2 performs a display operation based on the contents of each address in the internal memory of the programmable controller 5, the state of the internal relay, the value of the timer and the value of the counter. Each address of the memory corresponding to the information required in the display unit 2 and an internal relay are called "devices", and when the data representing the contents are handled in 1-word units, they are called "word devices". It is called “bit device” when it is handled in 1-bit units.

Data communication between the programmable controller 5 and each display 2 is performed via the link unit 6, the adapter 10 and the adapter 1. Adapter 10
And the adapter 1 includes a CPU (central processing unit), an EP
A ROM (erasable / writable read-only memory) and a communication IC are built in. All types of devices that may be required in the corresponding display unit 2 are registered in each adapter 1. Further, in the adapter 10, all types of devices that may be required for any display device 2 are registered. That is, all devices registered in the N adapters 1 are registered in the adapter 10.

The adapter 10 reads the contents of the devices of the programmable controller 5 according to the communication procedure in the link unit 6 and sends the read contents of all the devices to the dedicated line 8 at high speed. The contents of the device sent to the dedicated line 8 are respectively captured by the adapter 1 corresponding to each display unit 2. At this time, each adapter 1
Captures only the device content that the corresponding display 2 may need.

The display device 2 acquires the contents of the device required for display from the adapter 1 and performs the display operation according to the contents of the device. In this case, the display unit 2 operates by regarding the adapter 1 as a link unit, and the data communication between the adapter 1 and the display unit 2 is performed by the same communication procedure as the communication procedure in the link unit 6. Each indicator 2
Is capable of switching and displaying a plurality of screens, for example. One or more devices are assigned to each screen. A common device for switching screens and displaying abnormalities is assigned to a plurality of screens, and an individual device for each screen is also assigned. Hereinafter, a device commonly assigned to a plurality of screens is referred to as a “common device”, and a device assigned to each screen is referred to as an “individual device”.

[0011]

SUMMARY OF THE INVENTION For example, each display 2
Is capable of registering 500 screens from channel 1 to channel 500. In this case, if two individual devices are assigned to the screen of each channel without overlapping, one display device 2
Needs to acquire the contents of 1000 individual devices. Therefore, the adapter 1 holds the contents of 1000 individual devices. At this time, if, for example, 32 display devices 2 are connected to the adapter 10 via the adapter 1, the adapter 10 has a maximum of 32.
It is necessary to read the contents of 000 devices from the programmable controller 5.

The adapter 10 which is actually put to practical use
Can read and hold the contents of at most 2500 devices from the programmable controller 5. Therefore, assuming that 32 display units 2 are connected to the adapter 10, each display unit 2 has 78 (≈250).
Only 0/32) devices can be assigned. At this time, if an attempt is made to display a screen for 10 channels on each display 2, the number of individual devices that can be used for each screen will be about 7 to 8.

Therefore, in the above configuration, the number of screens that can be used on each display 2 and the number of devices that can be used on each screen are limited, and the display desired by the user cannot always be performed. It was Not only that, in the above-mentioned prior art, the link unit 6
The adapter 10 connected to must read from the programmable controller 5 the contents of all devices that may be needed in any display 2. Moreover, the data communication between the adapter 10 and the link unit 6 can be performed only at a low speed according to the communication procedure of the link unit 6. Therefore, the communication time between the programmable controller 6 and the adapter 10 becomes long, and there is also a problem that the display on each display 2 cannot be updated at high speed.

Since a large amount of data needs to be exchanged between the adapter 10 and the programmable controller 5, data communication between the adapter 10 and the link unit 6 is exclusively performed in word (16 bit) units. Is common. Therefore, it is possible to read the bit device, but it is practically impossible to change the content of the bit device from the display 2 side. In other words, even if the display unit 2 tries to rewrite only a specific 1 bit of the device in the programmable controller 5, the adapter 10 supplies 1-word data to the link unit 6, so that the remaining 15-bit value Cannot be kept at its original value.

In order to make this possible, the 16-bit contents including the bit device whose contents are to be changed are once read from the programmable controller 5, and only one bit of the read 16 bits is changed, and then the 16 bits are changed. Can be rewritten to the programmable controller 5. However, in this case, since it is necessary to once read out one word of data including the bit device, the communication speed becomes remarkably slow. Therefore, there is no example to which such a method is adopted so far.

Further, in order to increase the communication speed, the adapter 10 is configured to read the data of consecutive addresses from the programmable controller 5 and write the data of consecutive addresses to the programmable controller 5. Therefore, in order to prevent unnecessary data from being transmitted and received, it is necessary to use devices with consecutive numbers. That is, it is necessary to consider the continuity of devices in the programmable controller 5 when creating data for forming the display screen of the display 2.

In addition to these problems, in the above-mentioned prior art, it is necessary to provide one adapter 1 for each display unit 2, which causes a problem that the cost of the entire system increases. In addition, since it is necessary to individually register the device corresponding to the display content of the corresponding display device 2 in each adapter 1, the work before the start of use was extremely complicated.

Therefore, an object of the present invention is to solve the above-mentioned technical problem, to significantly reduce the amount of information to be retrieved from the host device, and to obtain the information from the host device for display operation in the display device. It is an object of the present invention to provide a communication device for a display device, which can achieve high speed and can increase the degree of freedom of display.

[0019]

A communication device for a display device according to the present invention for achieving the above object includes a plurality of display devices each capable of displaying one or more kinds of screens, and the plurality of display devices. Between the host device and the display device, which is interposed between the host device and the host device that holds the screen designation information for designating each display screen and the display information required for displaying each display screen. A communication device for a display device for exchanging information by means of a display device, the correspondence between the screen designation information and the type of display information necessary for displaying the display screen designated by the screen designation information. Management information storage means that stores the classified information for each display device, and a method for acquiring the screen designation information corresponding to the plurality of display devices from the host device according to the communication procedure on the host device side. And means for acquiring all kinds of display information corresponding to the acquired screen designation information from the host device according to the communication procedure of the host device side by referring to the stored contents of the management information storage device. And means for distributing the display information acquired from the host device to the plurality of display devices.

[0020]

Each display device performs a display operation based on the information held by the host device. However, the information actually required by each display device at a certain moment is displayed by the display device on an arbitrary display screen. It is only part of all the information that may be needed to make a presentation.

According to the present invention, the correspondence between the screen designation information for designating the display screen and the display information required for displaying the display screen designated by the screen designation information is classified for each display device. It is stored in the management information storage means. Then, the screen designation information for designating the display screens of the plurality of display devices is acquired from the display device, and all kinds of display information corresponding to the acquired screen designation information are processed according to the communication procedure on the host device side. , Obtained from the host device. This acquired information is distributed to each display device.

In this way, according to the present invention, only the display information actually needed to display the display screen to be displayed on the plurality of display devices is acquired from the host device. Therefore, the amount of information acquired from the host device according to the communication procedure on the host device side is extremely small. Therefore, the communication time with the host device is shortened, and the display speed can be increased.

The information acquired from the host device is
Only the information that the multiple display devices actually need is acquired, and not all the information that may be needed by the multiple display devices is acquired. Therefore, even when the amount of all the information that may be required by the plurality of display devices is extremely large, a problem occurs unless the amount of information required by the plurality of display devices is large at the same time. There is no such thing. Therefore, each of the display devices can obtain various types of information from the host device with almost unlimited display. As a result, the display desired by the user can be realized without any restrictions.

[0024]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a conceptual configuration of a display system to which a communication device according to an embodiment of the present invention is applied. A programmable controller 31 as a host device is provided with a plurality of display devices D1, D2, D via a link adapter 32 which is a communication device of this embodiment.
3, ..., Dk (hereinafter, referred to as “display device D” when collectively referred to, for example, k = 32) are connected. More specifically, the link adapter 32 is the link unit 3 mounted on the programmable controller 31.
Data communication with the programmable controller 31 is performed via The data communication at this time is performed at a relatively low speed according to the communication procedure of the link unit 33. On the other hand, the link adapter 32 and the plurality of indicators D1, D2, D
Data communication with 3, ..., Dk is performed at high speed by a dedicated protocol using the dedicated line 35.

The display D is capable of registering data of up to 500 screens from channel 1 to channel 500, for example. The data of each screen is created using a personal computer and then downloaded to the display device D. The same display screen is rarely used in a plurality of display devices D, and generally, different screens are registered in each display device D.

The display D has a memory table inside, and performs a display operation according to the contents of this memory table. The contents of so-called devices such as predetermined addresses of memories in the programmable controller 31, internal relays and timers are written in the memory table. That is,
The display device D displays according to the contents of the devices in the programmable controller 31.

Table 1 below shows an example of device contents and device names in the programmable controller 31. In Table 1, each device is shown by being divided into a word device and a bit device. For example, input data and output data can be handled as word devices and bit devices.

[0028]

[Table 1]

In each screen registered in the display device D, there are a common device commonly used for each screen such as for screen switching and an error message display, and an individual device individually used for each screen. It is associated. That is, devices corresponding to these functions are associated with all screens so that display screens can be switched and abnormal messages can be displayed commonly on any screen.
Then, for example, devices corresponding to the functions of displaying numerical values and displaying graphs are associated with individual screens as necessary.

The device for switching the screen is a predetermined storage area of the memory in the programmable controller 31. The content of this device is a display screen number as screen designation information for designating a display screen. That is,
The memory in the programmable controller 31 stores a plurality of display screen numbers respectively corresponding to the plurality of display devices D. When switching the display screen of the display D, the display screen number is rewritten.

The contents of the above-mentioned device for displaying an abnormal message and the device corresponding to the numerical value display and the graph display correspond to the display information. FIG. 2 is a block diagram showing a simplified internal configuration of the link adapter 32. The link adapter 32 includes a CPU 41. C
An RS485 interface driver 42 for connecting the dedicated line 35 connected to the display D is connected to the PU 41, and an RS422 interface for connecting a host device such as the programmable controller 31 or a personal computer. Driver 4
3 and RS232C interface driver 44 are connected via a switching circuit 45.

The bus 48 connected to the CPU 41 has a C
A ROM 51 in which an operation program of the PU 41 is stored, a RAM 52 used as a work area, etc., and a data flash EPROM 53 as a management information storage unit in which information necessary for data communication with the programmable controller 31 and the display D is registered. , Data RAM
54 and the DIP switch 55 are connected.

FIG. 3 shows a flash EPROM 5 for data.
3 is a diagram for explaining the content of data registered in FIG. In the data flash EPROM 53, all device names that may be required by an arbitrary display device D are registered. This device name is classified and registered for each display device D. Then, a common device name required for displaying all the display screens on the display device D is registered corresponding to each display device D, and further, is required for displaying each individual display screen. The individual device name is stored in association with the display screen number.

In FIG. 3, for example, a common device D0100 corresponding to the display D1 is a device for switching the screen of the display D1, and a common device D0101 corresponding to the display D2 is a device for switching the screen of the display D2. And a common device D0102 corresponding to the display device D3.
Is a device for switching the screen of the display D3. The device name table as described above is created in advance in a personal computer (not shown), and the data flash EPR is transmitted via the interface driver 43 or 44.
It has been downloaded to OM53. At the time of this download, by setting the DIP switch 55, the CPU
41 performs an operation of writing the data from the interface driver 43 or 44 into the data flash EPROM 53.

FIG. 4 is a flow chart for explaining the operation of the link adapter 32. Link adapter 32
First, via the link unit 33, a device for switching the screen in the programmable controller 31 (see FIG.
In the example, D0100, D0101, D0102, ...
Acquire the contents of the common device including (step S
1). That is, the display screen numbers of all the display devices D1, D2, ..., Dk are acquired from the programmable controller 31 according to the communication procedure of the link unit 33. Based on the display screen number of each display device D thus obtained, the CPU 41 refers to the contents of the flash EPROM 53 to read the device name associated with the display screen number of each display device D (step S2).

Next, the CPU 41 sorts the read device names (step S3). For example, assume a case where three display devices D1, D2, D3 are connected to the dedicated line 35. At this time, it is assumed that the display screen number of the display device D1 is CH1, the display screen number of the display device D2 is CH3, and the display screen number of the display device D3 is CH10. It is assumed that the following device names are assigned to the display screen number CH1 of the display device D1, the display screen number CH3 of the display device D2, and the display screen number CH10 of the display device D3.

CH1 D0300, D0302 of display D1 CH3 D0200, D0202 of display D2 CH10 D0310, D0312 of display D3 In this case, the device names are sorted, for example, in ascending order, and rearranged as follows. .

D0200, D0202, D0300, D0302, D0310, D0312 After such sort processing, the CPU 41 further divides the device names into device names whose numbers are relatively close to each other, and continuously includes the groups. Then, the smallest device area is found (step S4). That is, in the above example, for example, devices D0200 and D0
A first group including 0202 and a device D0300,
The device names are grouped into a second group including D0302, D0310, and D0312. The area D0 is set as the smallest continuous area including the first group.
200 to D0202 are found, and areas D0300 to D0312 are found as the smallest continuous area including the second group.

For each continuous area thus obtained, the link adapter 32 reads out the contents of the device in the programmable controller 31 via the link unit 33 (step S5). In this case, the link adapter 32
According to the communication procedure of the link unit 33, the communication with the programmable controller 31 is performed twice.
That is, the data communication corresponding to the two continuous areas corresponding to the first group and the second group is performed.

If the sorting process of step S3 and the continuous area finding process of step S4 are omitted and communication is performed with the programmable controller 31 for each device, in the above example, 6 It is necessary to perform the processing according to the communication procedure of the link unit 33 over a number of times. Therefore, the communication time may be extremely long.

The data acquired in step S5 is temporarily stored in the data RAM 54. And the CPU 41
Refers to the data flash EPROM 53, and displays data representing the contents of the common device, such as the display screen number of each display D, and data corresponding to the contents of the individual device corresponding to the display screen number. Distribute to D (step S6). The subsequent process returns to step S1.

Each display D takes in the data given from the link adapter 32 to the internal memory table via the dedicated line 35, and performs the display operation based on the contents of this memory table. The data communication between the link adapter 32 and the display unit D does not need to follow the communication procedure of the link unit 33, and therefore is performed at high speed using another high-speed dedicated communication protocol.

FIG. 5 is a diagram for explaining the number of devices for which the link adapter 32 communicates with the programmable controller 31 to acquire the contents. In order to simplify the explanation, the dedicated line 35 has four indicators D1, D2,
D3 and D4 are connected to each display D1, D2, D
It is assumed that screen data for 6 screens from channels 1 to 6 is registered in D3 and D4. Further, the contents of the 20 individual devices in the programmable controller 31 are used for displaying each screen of each display D, and the individual devices required for displaying each display screen do not overlap each other. Suppose

In this case, in order to display all four display devices D1, D2, D3, D4 at a certain moment, the contents of 80 (= 20 × 4) individual devices are programmed by the programmable controller. It is sufficient to read from 31. For example, assume that when the link adapter 32 inquires the programmable controller 31 about the display screen numbers of the displays D1, D2, D3, D4, CH1, CH2, CH3, CH4 are acquired as the display screen numbers of the respective display devices D. . In this case, the link adapter 32 has contents of 80 individual devices corresponding to the display screen numbers of the respective display devices D (actually, the contents of devices in a certain continuous area are read out, so the contents are 80 or more). From the programmable controller 31.

Under the same premise, in the prior art shown in FIG. 6, the adapter connected to the link unit of the programmable controller has a minimum of 480.
The contents of (= 20 × 6 × 4) individual devices are read from the programmable controller. As is apparent from this comparison, according to the present embodiment, it is understood that the number of devices whose contents are read from the programmable controller 31 is extremely small. As a result, the communication time with the programmable controller 31 can be significantly shortened as compared with the conventional technique.

Since the number of devices that acquire contents from the programmable controller 31 is small, data communication is also performed in bit units in this embodiment. That is, in the related art, since it was necessary to read the contents of a large amount of devices from the programmable controller 31 to the adapter, the bit-unit data communication was sacrificed. On the other hand, in the configuration of the present embodiment in which the number of devices read from the programmable controller 31 is extremely reduced and the communication time with the programmable controller 31 is significantly shortened, even if data communication in bit units is performed, each display unit D is displayed. The display speed in can be kept sufficiently high.

The bit-unit data communication will be described in detail by taking the switch operation as an example. The switch operation is, for example, turning on / off a lamp (not shown) connected to the programmable controller 31 in response to an operation of a switch (not shown) such as a touch panel or a function switch attached to the display D1. It is an operation to turn off the light. In order to enable such an operation, the link adapter 32 performs a communication process for acquiring data to be given to the programmable controller 31 from each display D at predetermined time intervals.

Assume, for example, that a predetermined lamp connected to the programmable controller 31 is turned on by writing data "1" to the bit device Y0002. In this case, the link adapter 32 performs communication in 1-bit units with the programmable controller 31 via the link unit 33 based on the acquisition of such data from any one of the display devices D.
Data "1" is written in bit device Y0002.

For comparison, it is assumed that only word-by-word communication is possible as in the prior art. In this case, 16 bits Y0000 to Y000F are the communication units. In this case, since the adapter side connected to the link unit cannot know the original values of Y0000 to Y000F, the data of the bit device Y0002 can be determined to be "1", but the remaining bit Y
The data of 0000, Y0001, Y0003 to Y000F cannot be determined. Therefore, the remaining bit Y0
It is conceivable that the data "1" or the data "0" is uniformly written in 000, Y0001, Y0003 to Y000F, but in this case, it is possible that the values of those bits cannot be held at the original values. Is high. That is, if the data “1” is written to the bit device Y0002, the value of the peripheral bits will be rewritten.

Such a problem does not occur in this embodiment in which communication can be performed in bit units. As described above, according to the present embodiment, the number of devices read from the programmable controller 31 to the link adapter 32 at one time is significantly smaller than that in the conventional technique. Therefore, the communication time between the programmable controller 31 and the link adapter 32 becomes extremely short, and the display on the display D can be performed at high speed.

Since the number of devices read from the programmable controller 31 and temporarily held in the link adapter 32 is small, a large number of screens are registered in each display and a large number of devices are stored in each screen. Even if it is set to use the contents, the link adapter 3
There is no shortage of the storage capacity of 2. As a result, the number of display screens and display contents are not limited, and the display desired by the user can be reliably realized.

Furthermore, only the contents of the small number of devices currently required for display on the plurality of displays D are read from the programmable controller 31, and
Since it is possible to read out the device contents of the discontinuous area, it is not necessary to consider the continuity of the devices used in the plurality of display devices D. Therefore, the degree of freedom in creating the data necessary for display on the display device D increases.

Moreover, if the link adapter 32 is provided,
Since it is not necessary to separately provide an adapter for each display unit D, it can contribute to cost reduction, and the device name required by each display unit can be individually registered for the adapter corresponding to each display unit. There is no need to do any work. That is, it is sufficient to prepare only the link adapter 32 and collectively register the device name information corresponding to all the display devices in the link adapter 32.

Furthermore, as described above, the programmable controller 31 can be operated without significantly impeding the high speed communication.
Since it is also possible to communicate with each other in bit units, the function of the display device D can be fully utilized. The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, in the above-described embodiment, the device name that may be required by each display is pre-downloaded to the flash EPROM 53 in the link adapter 32, but the following method may also be adopted. it can. That is, in response to the power-on of the link adapter 32, the function of the CPU 41 inquires of each display device D about the device name that may be necessary and acquires it. Then, the information acquired by the inquiry is registered in the flash EPROM 53. By doing so, the registration of data in the flash EPROM 53 can be automated.

In the above embodiment, the case where the programmable controller is used as the host device has been described, but a personal computer or the like may be used as the host device. Further, in the above example,
An example in which a plurality of display devices are connected to one host device via a link adapter has been described. However, even if a plurality of host devices and a plurality of display devices are connected via the link adapter. Good. In this case, the indicator is
It is possible to acquire information necessary for display from a plurality of host devices.

In addition, various design changes can be made without changing the gist of the present invention.

[0057]

As described above, according to the present invention, only a small amount of information that is actually needed for displaying a screen on a plurality of display devices is acquired from the host device, so that communication with the host device is possible. The time is shortened, and the display on the display device can be speeded up. Also, since the information acquired from the host device is only the information that is actually needed for screen display on a plurality of display devices, it is possible that a plurality of display devices may need it for arbitrary screen display. Even if the amount of all certain information is extremely large, no problem will occur unless the amount of information required by a plurality of display devices at the same time is large. Therefore, in each display device, various kinds of information can be freely obtained and displayed from the host device almost without limit. As a result, the display desired by the user can be reliably realized, and the degree of freedom of display on the display device can be increased.

Further, the data communication between the communication device and the display device does not need to follow the communication procedure on the host device side, and another high speed dedicated procedure can be adopted. By doing so, the display operation can be further speeded up.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a display system to which a link adapter that is a communication device according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing an internal configuration of a link adapter.

FIG. 3 is a diagram for explaining the content of data registered in a data flash EPROM.

FIG. 4 is a flowchart for explaining the operation of the link adapter.

FIG. 5 is a diagram for explaining the number of devices for which a link adapter should acquire contents from a programmable controller.

FIG. 6 is a block diagram showing a configuration of a conventional display system.

[Explanation of symbols]

 31 programmable controller 32 link adapter 33 link unit 35 dedicated line D1, D2, ..., Dk display 41 CPU 42 RS485 interface driver 43 RS422 interface driver 44 RS232C interface driver 45 switch 53 data flash EPROM 54 data RAM

Claims (1)

[Claims] 1. A plurality of display devices capable of respectively displaying one or more types of screens, screen designation information for designating the display screens of the plurality of display devices, and necessary for displaying each display screen. A communication device for a display device, which is interposed between a host device that holds display information and is used for exchanging information between the host device and the display device, And a management information storage unit that stores the correspondence relationship between the types of display information required for displaying the display screen specified by the screen specifying information for each display device, and the plurality of displays. A means for acquiring the screen designation information corresponding to the device from the host device in accordance with the communication procedure on the host device side, and the acquired screen designation by referring to the stored contents of the management information storage means. Means for obtaining all types of display information corresponding to the information from the host device according to the communication procedure of the host device side, and distributing the display information obtained from the host device to the plurality of display devices. A communication device for a display device, comprising: