JP2856005B2 - Data communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication method, and more particularly, to a data communication method capable of reducing the overhead of an external device that issues an access request to an access requesting data link unit.

[0002]

2. Description of the Related Art FIG. 17 is an essential part extraction diagram of a communication system 500 according to a conventional data communication method. The access request source data link unit 1301K is
302K and a link processing unit 1303K. The data processing unit 1302K includes a data line 131
9 is connected to an external device 1304K. Further, the link processing unit 1303K communicates with the access request destination data link unit 1320K via the communication line 1318.
It is connected to the. An information terminal 1400 is connected to the access request destination data link unit 1320K.

[0003] The data processing unit 1302K includes a CPU and an R
It comprises an OM, a RAM, a bus I / F, and an external device I / F, and each unit is connected by an internal bus. The link processing unit 1303K includes a CPU, a ROM, a RAM, a bus I / F, a communication I / F, and a dual port RAM 13
16K, and each unit is connected by an internal bus.

FIG. 18 shows a dual port RAM 1316.
FIG. 3 is an internal configuration diagram of K. Request data buffer 1401K
Consists of an access request destination station number column for storing the identification number of the access request destination data link unit 1320K and an access request content column for storing the content of the access request (or transmission request). Answer data buffer 1402K
Consists of an access request destination station number column and a data column for storing data corresponding to the access request.

Next, a communication sequence of the communication system 500 shown in FIG. 17 will be described with reference to FIG. In addition,
In FIG. 19, <1>,..., <12> indicate phases in the communication sequence. First, the operation of the external device 1304K is shown in FIG. In step S1501, the external device 1304K and the access request source data link unit 1
An “access request” requesting data that can be exchanged with the access request 301K at one time is output to the access request source data link unit 1301K (phase <1>). In step S1502, the process stands by until data is received (phase <2>).

Next, the operation of the data processing unit 1302K of the access request source data link unit 1301K will be described.
As shown in FIG. In step S1601, the external device 13
Perform processing other than communication with 04K (unique processing unrelated to the access request).

In step S1602, the external device 130
It is determined whether an “access request” from 4K has been received. Upon receiving the “access request”, step S1603
If the “access request” has not been received, the process proceeds to step S1604. In step S1603, “access request” is transferred to link processing section 1303K (phase <3>). In step S1604, the process waits until “data” is stored in the dual port RAM 1316K of the link processing unit 1303K. Then, the “data” is transferred to the external device 1304K (phase <2>). In step S1605, the link processing unit 13
03K is set as the communication content that is always performed (the communication content that is performed even without a request from the data processing unit 1302K).

Next, the operation of the link processing unit 1303K of the access request source data link unit 1301K will be described.
As shown in FIG. In step S1701, communication that is always performed with the data processing unit 1302K is performed.

In step S1702, the data processing unit 1
It is determined whether an “access request” from 302K has been received. When an "access request" is received, it is transferred to the request data buffer 1401K of the dual port RAM 1316K.
Then, the process proceeds to step S1703, and if the “access request” is not received, the process proceeds to step S1706.

In step S1703, the access request destination data link unit 1320K is determined from the access request destination station number column of the dual port RAM 1316K. In step S1704, the data processing unit 1302K
Is notified of the "access request" (not shown).
In step S1705, based on the received “access request”, the access request destination data link unit 132
"Transmission request" is output at 0K (phase <5>).

In step S1706, a "storage check" requesting delivery of the "data" stored in access request destination data link unit 1320K is output (phase <6>). Note that the access request destination data link unit 1320K replies “unstored response” if “data” is not stored (phase <7>), and returns “data” if it is stored (phase <8). 〉).
In step S1707, “data” is received from the access request destination data link unit 1320K and stored in the dual port RAM 1316K (phase <8>). In step S1708, “data” is read from the dual port RAM 1316K, and output to the external device 1304K via the data processing unit 1302K (phase <4>) (phase <2>). Step S
At 1709, the processing result by the data processing unit 1302K is set by the communication always performed with the data processing unit 1302K.

Next, the operation of the link processing unit of the access request destination data link unit 1320K is shown in FIG. In steps S2801 and S2802, communication that is always performed with the data processing unit is performed, and a processing result by the data processing unit is set.

In step S2803, it is determined whether a “transmission request” has been received from the access request source data link unit 1301K. If a "transmission request" has been received, the process proceeds to step S2804, and if a transmission request has not been received, the process proceeds to step S2805. Step S280
In 4, the "transmission request" is set in the dual port RAM, and the process returns to step S2801. Thereby, the “transmission request” is transmitted to the data processing unit (phase <9>).

In step S2805, the data processing unit determines whether or not “data” for the “transmission request” has been received from information terminal 1400. If it has been received, the process proceeds to step S2806; otherwise, the process proceeds to step S2806.
Return to 2801. In step S2806, the received “data” is stored in the data column of the dual port RAM (phase <10>).

In step S 2807, “access check” is issued from the access request source data link unit 1301 K.
Waits for receiving, and upon receipt, step S2808
Proceed to. In step S2808, “data” is transmitted to access request source data link unit 1301K (phase <8>), and the flow returns to step S2801.

Next, the operation of the data processing unit of the access request destination data link unit 1320K is shown in FIG. In step S2901, processing other than communication (processing unique to the data processing unit) is performed.

In step S2902, it is determined whether a "transmission request" has been received from the link processing unit. If it has been received, the process proceeds to step S2903, and if it has not been received, the process proceeds to step S2905. In step S2903, processing for the "transmission request" is performed, such as outputting the received "transmission request" to information terminal 1400 (phase <11>). In step 2904, the information terminal 1400
(Phase <12>), and outputs the data to a link processing unit having a dual port RAM (phase <10>). In step S2905, communication that is always performed with the link processing unit is performed.
Return to

[0018]

In the above conventional data communication method, the amount of data required by the external device is reduced.
If the amount of data is larger than the amount of data that can be exchanged at one time between the external device and the access request source data link unit, the external device outputs an access request requesting the amount of data that can be exchanged at one time. It is necessary to wait until data is received and repeat this series of processing until all data is received. Therefore, there is a problem that the external device cannot perform other processes from outputting the access request to receiving the data, so that the overhead becomes large and the entire processing time becomes long.

Accordingly, an object of the present invention is to reduce the overhead of an external device when the required data amount is larger than the data amount that can be exchanged between the external device and the access requesting data link unit at one time. It is an object of the present invention to provide a data communication method capable of reducing the processing time and the entire processing time.

[0020]

According to a first aspect, the present invention provides a data communication system connected to an external device via a data line.
Data link via the data processing unit and the communication line.
The external device with respect to accession <br/> Seth requesting data link unit comprising the connected and a link processing section click unit
The access request source data link unit transmits the access request to the access request destination data link unit having a data processing unit and a link processing unit via the communication line in response to the access request. In a data communication method for issuing a request, receiving data from the access request destination data link unit, and passing the data to the external device, the external device sends the access request source data link unit a full range of required data ( An access request for requesting the entire range of data amount> the amount of data that can be exchanged between the external device and the access request source data link unit at a time) is output, and then the entire range of data is sent to the access request source data link unit. Until the data is collected, the other processing is executed. Wherein the original data link unit sequentially 1
The access request source data link unit issues a transmission request to the access request destination data link unit in response to the access request, and receives the data via the communication line. And transferring the entire range of data to the external device by the amount of data that can be exchanged at a time when the entire range of data is completed. Provide a communication method.

In a second aspect, according to the present invention, an external device inquires of an access requesting data link unit whether or not data in the entire range has been prepared while executing other processing. The data communication method is characterized in that the access requesting data link unit reports a response as to whether or not the entire range of data has been prepared or a degree of data preparation.

In a third aspect, according to the present invention, the access request source data link unit notifies the external device of the data buffer full when the data buffer becomes full before the data in the entire range is prepared. In response to the data buffer full notification, the external device starts receiving data stored in the access requesting data link unit up to that time.

[0023]

In the data communication method according to the first aspect, the external device sends the entire range of required data (total data amount> the external device and the access request source data link) to the access request source data link unit. After outputting an access request for requesting the amount of data that can be exchanged with the unit at one time), other processing can be executed until the entire range of data is available in the access request source data link unit, thereby reducing overhead. it can. Further, since the entire range of data is sequentially received from the access request source data link unit having the entire range of data, the waiting time is shortened, and the overall processing time can be shortened. Furthermore,
Access request source data link unit and access request
Data processing unit of destination data link unit requests access
You can extend the time it takes to do some unrelated processing
Thus, the efficiency of the data processing unit can be improved.

[0024] In the data communication method according to the second aspect, the external device can determine whether or not the entire range of data has been prepared or the degree of data preparation while performing other processing. I can receive it.

In the data communication method according to the third aspect, when the external device is notified that the data buffer of the access request source data link unit has become full,
Since the reception of the data stored in the access request source data link unit is started, the loss of the data stored in the data buffer can be prevented.

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It should be noted that the present invention is not limited by this.

First Embodiment FIG. 1 is an essential part of a communication system 100 for implementing a data communication method according to a first embodiment of the present invention. As a specific example of the communication system 100, for example, “MELSECNET
(Mitsubishi Electric).

Access request source data link unit 13
01A includes a data processing unit 1302 and a link processing unit 13
03. The data processing unit 1302
Via the data line 1319 (such as RS232C)
It is connected to an external device 1304A. The link processing unit 1303 is connected to an access request destination data link unit 1320 via a communication line 1318. An information terminal 1400 is connected to the access request destination data link unit 1320. The access request source data link unit 1301A and the access request destination data link unit 1320 may have the same configuration.

The data processing unit 1302 includes a CPU, an RO,
M, a RAM, a bus I / F, and an external device I / F, and each unit is connected by an internal bus. The link processing unit 1303 includes a CPU, a ROM, a RAM,
/ F, communication I / F, dual port RAM 1316
A, and each section is connected by an internal bus.

FIG. 2 shows a dual port RAM 1316A.
FIG. Request data buffer 1401A
Consists of an access request destination station number field for storing the identification number of the access request destination data link unit 1320 and an access request content field for storing the content of the access request (or transmission request). The answer data buffer 1402A
In this configuration, an access request destination station number column and a data column for storing data corresponding to the access request are stacked.

Next, a communication sequence of the communication system 100 shown in FIG. 1 will be described with reference to FIG. Note that FIG.
, [1],... [16] indicate phases in the communication sequence. First, the operation of the external device 1304A is described as follows.
As shown in FIG. In step S201, an “access request” requesting data in the entire required range is output to the access requesting data link unit 1301A (phase [1]). However, the data amount in the entire range> external device 1304
A is the data amount that can be exchanged at a time between A and the access requesting data link unit 1301A.

In step S202, other processing (processing not related to an access request, for example, data processing by an internal program) is executed.

In step S203, a "storage confirmation" is output to inquire whether the entire range of data has been stored in the dual port RAM 1316A of the access requesting data link unit 1301A (phase [2]).

In step S204, the contents of a response from the access request source data link unit 1301A are determined. If the response content is "notification of incomplete" (data to be stored remains) (phase [3]), step S2
Return to 02. If the response content is the first "data" (phase [4]), the process proceeds to step S205.

In step 205, the first "data" is received. In step 206, the "transmission request" of "data" (the amount of data that can be exchanged at one time) is output to the access requesting data link unit 1301A (phase [5]). In step S207, “data” is received from the access request source data link unit 1301A (phase [6]). In step S208, it is determined whether the entire range of data has been received. If the data in the entire range has been received, the process ends. If data to be received remains, the process returns to step S206.

FIG. 5 shows the operation of the data processing unit 1302 of the access request source data link unit 1301A. In step S301, the external device 1304A
Performs processing other than communication with the server (specific processing unrelated to the access request).

In step S302, the external device 1304
It is determined whether an “access request” from A has been received.
If an “access request” is received, the process proceeds to step S303. If an “access request” is not received, the process proceeds to step S303.
Proceed to 304. In step S303, the “access request” is transferred to the link processing unit 1303 (phase [7]).

In step S304, the external device 1304
It is determined whether or not “storage confirmation” from A has been received.
When the “storage confirmation” is received, the process proceeds to step S305,
If “storage confirmation” has not been received, the process proceeds to step S308.

In step S305, the dual port R
It is determined whether the entire range of data is stored in AM1316A. If the data in the entire range has been stored, the process proceeds to step S306, and if data to be stored remains, the process proceeds to step S307. In step S306, a “transmission request” requesting transmission of the first “data” is output to link processing section 1303 (phase [8]). Thereby, the first “data” is transferred to the external device 1304A (phase

[9], [4]). In step S307, an “incomplete notification” is transmitted to the external device 1304A (phase [3]).

In step S308, the external device 1304
It is determined whether the “transmission request” from A has been received. If a "transmission request" has been received, the process proceeds to step S309. If a "transmission request" has not been received, the process returns to step S301.
In step 309, the received “transmission request” is transferred to the link processing unit 1303. As a result, the “data” corresponding to the “transmission request” is transferred to the external device 1304A (phase

[9], [6]). In step S310,
The contents of communication that is always performed with the link processing unit 1303 (the contents of communication that is performed even without a request from the data processing unit 1302) are set, and the process returns to step S301.

FIG. 6 shows the operation of the link processing unit 1303 of the access request source data link unit 1301A. In step S401, the data processing unit 130
Communication between the two is always performed.

In step S402, the data processing unit 13
It is determined whether or not an “access request” has been received. If an "access request" is received, it is stored in the request data buffer 1401A of the dual port RAM 1316A and the process proceeds to step S403. If an "access request" is not received, the process proceeds to step S405. Step S
At 403, the access request destination data link unit 1320 is determined from the access request destination station number column of the dual port RAM 1316A. In step S404, the data processing unit 1302 is notified of the receipt of the “access request” (not shown), and the process proceeds to step S411.

In step S405, it is determined whether or not "data" is stored in the dual port RAM of the access request destination data link unit 1320. If it is stored, the process proceeds to step S406; otherwise, the process proceeds to step S412. In step S406,
It outputs a “storage check” requesting delivery of the “data” stored in the access request destination data link unit 1320 (not shown). In step S407, “data” is received from the access request destination data link unit 1320, and stored in the dual port RAM 1316A (phase [12]).

In step S408, it is determined whether the entire range of data has been stored in the dual port RAM 1316A. If the entire range of data is stored, step S40
9 and if there is data to be stored, step S
Proceed to 411.

In step S409, the data corresponding to the received "transmission request" is stored in the dual port RAM 1316A.
And outputs it to the external device 1304A via the data processing unit 1302 (phase

[9], [4] or [6]). In step S410, it is determined whether the entire range of data has been output to external device 1304A. After outputting the data in the entire range, the process proceeds to step S412, and if there is data to be output, the process returns to step S409.

In step S411, a "transmission request" is output to the access request destination data link unit 1320 based on the received "access request" (phase [1]).
1)). However, the data amount for the transmission request <the data amount that can be exchanged at one time between the access request source data link unit 1301A and the access request destination data link unit 1320.

In step S412, the data processing unit 13
02, the data processing unit 130
The processing result of step 2 is set, and the process returns to step S401.

Next, the operation of the link processing unit of the access request destination data link unit 1320 is shown in FIG.
In steps S1801 and 1802, communication that is always performed with the data processing unit is performed, and a processing result by the data processing unit is set.

In step S1803, it is determined whether a "transmission request" has been received from access request source data link unit 1301A. If a "transmission request" has been received, the process proceeds to step S1804, and if a transmission request has not been received, the process proceeds to step S1805. Step S180
In step 4, "transmission request" is set in the dual port RAM, and the flow returns to step S1801. Thereby, the “transmission request” is transmitted to the data processing unit (phase [1]
3]).

In step S1805, the data processing unit determines whether or not “data” for the “transmission request” has been received from information terminal 1400. If it has been received, the process proceeds to step S1806, and if it has not been received, the process proceeds to step S1806.
Return to 1801. In step S1806, the received “data” is stored in the data column of the dual port RAM.

In step S1807, the storage request is sent from the access request source data link unit 1301A.
Waits for receiving, and upon receipt, step S1808
Proceed to. In step S1808, “data” is output to access request source data link unit 1301A (phase [12]).

Next, the operation of the data processing unit of the access request destination data link unit 1320 is shown in FIG.
In step S1901, processing other than communication (processing unique to the data processing unit) is performed.

In step S1902, it is determined whether a "transmission request" has been received from the link processing unit. If it has been received, the process proceeds to step S1903, and if it has not been received, the process proceeds to step S1905. In step S1903, processing for the “transmission request” is performed, such as outputting the received “transmission request” to the information terminal 1400 (phase [15]). In step 1904, the information terminal 1400
("Phase [16])" and outputs it to a link processing unit having a dual port RAM (Phase [14]). In step S1905, communication that is always performed with the link processing unit is performed.
Return to

Next, the effect of the first embodiment will be verified with a specific example. However, the following preconditions are assumed for convenience of explanation. (1) The amount of data in the entire range is the amount of data that needs to be exchanged 100 times between the external device and the access request source data link (and between the access request source data link unit and the access request destination data link unit). And (2) In the conventional example, ta = tb = tc = 10 ms, td = 5 ms (FIG. 19), and the other required time is ignored. (3) In the first embodiment, t1 = 10 ms, t2 = 10 ms, t3 = 2 ms, t4 = 5 ms,
t5 = 5 ms, t6 = 10 ms (FIG. 3), and ignore the other required time.

Therefore, the data receiving time tp = (ta + tb + tc + td) * 100-td = 3495 ms for the conventional external device 1304K to receive “data” in the entire range is overhead. On the other hand, in the external device 1304A of the first embodiment, other processing can be executed during the preparation time tq = t1 + (t2 + t3) * 100 + t4 = 1215ms until the entire range of data is prepared. . Also, the data reception time tr = (t5 + t6) * 100-t5 = 1495 ms for receiving the entire range of data from the access request destination data link unit 1320 is an overhead, but is 2000 ms (= tp- t
r) only short. Furthermore, the total processing time is 2710ms (= tq + tr)
And it can be shortened by 785ms (= tp-tr) compared to the conventional example.

According to the first embodiment, since other processing can be executed until the entire range of data required by the external device is collected in the access requesting data link unit, the overhead can be reduced. Further, since the data is collectively received after the data in the entire range is prepared, the overall processing time can be reduced.

Second Embodiment FIG. 9 is a view corresponding to FIG. 1 of a second embodiment of the present invention. The communication system 200 according to the second embodiment of the present invention has substantially the same configuration as the communication system 100 shown in FIG. 1, but is different from the first embodiment in that an access requesting data link unit 1301B having a dual port RAM 1316B is used. It is different from the example.

FIG. 10 shows a dual port RAM 1316.
4 is an internal configuration diagram of B. FIG. This dual port RAM 13
16B is the dual port RAM 1316 shown in FIG.
The configuration is almost the same as A, but a new data storage degree area 61 for storing the degree of data alignment is newly provided.

Next, referring to FIG.
The communication sequence of 0 will be described. The communication system 2
The communication sequence of 00 is almost the same as the communication sequence of the communication system 100 of the first embodiment (FIG. 3), but the operation of the link processing unit 1303 of the access requesting data link unit 1301B is different.

FIG. 12 is an operation flowchart of the link processing unit 1303 of the access request source data link unit 1301B. Steps S401 to S407 are the same processing as steps S401 to S407 in FIG. Step U
At 1, the degree of data alignment is counted, and the data storage degree area 61 of the dual port RAM 1316B is counted.
To memorize.

In step S408 ', it is determined whether the entire range of data has been stored in the dual port RAM 1316B. If the entire range of data is stored, step S4
09, and if data to be stored remains, the process proceeds to step U2.

Steps S409 to S412 are the same processing as steps S409 to S412 in FIG. In step U2, the progress (dual port RAM 1316B
Is output to the external device 1304A via the data processing unit 1302 (phase [a]) (phase [b]).

In the second embodiment, the dual port RA
It is assumed that only the degree of data alignment before the entire range of data is aligned in M1316B is output to external device 1304A as an intermediate process, but data stored up to that point may also be output.

According to the second embodiment, the external device 130
The 4A can receive the degree of data alignment in the dual port RAM 1316B as an intermediate process, so that the storage confirmation output interval can be adjusted and the operator can be notified of the waiting time until the entire range of data is aligned. .

Third Embodiment FIG. 13 is a view corresponding to FIG. 9 of a third embodiment of the present invention.
The communication system 300 according to the third embodiment of the present invention has substantially the same configuration as the communication system 200 shown in FIG. 9, except that an access requesting data link unit 1301C having a dual port RAM 1316C is used. It is different from the example.

FIG. 14 shows a dual port RAM 1316.
It is an internal block diagram of C. This dual port RAM 13
16C is the dual port RAM 131 shown in FIG.
6B, but has a memory shortage notification area 111 for monitoring buffer fullness.

Next, referring to FIG.
The communication sequence of 0 will be described. The communication system 3
The communication sequence of 00 is almost the same as the communication sequence of the communication system 200 of the second embodiment (FIG. 11), but the operation of the link processing unit 1303 of the access requesting data link unit 1301C is different.

FIG. 16 is an operation flowchart of the link processing unit 1303 of the access request source data link unit 1301C. Steps S401 to S407 and step U
1 is the same process as steps S401 to S407 in FIG. 12 and step U1. In step V1, the memory shortage notification area 111 is referred to
It is determined whether the answer data buffer 1402A of 1316C is buffer full (or buffer full is near). If the buffer is full, the process proceeds to step S409. If the buffer is not full, the process proceeds to step S408 '. Step S408 ', Step U2, and Steps S409 to S412 correspond to Step S408' in FIG.
And Step U2 and the same processing as Steps S409 to S412. Therefore, when the buffer is full, the "data" stored in the dual port RAM 1316C at that time is output to the external device 1304A via the data processing unit 1302 (phase [c], [ d]).

According to the third embodiment, in addition to the effects of the second embodiment, the dual port RAM 1316C
Can be prevented from being lost due to the buffer full.

In the first to third embodiments, the link processing unit 1303 has the dual port RAMs 1316A to 1316.
C, the data processing unit 1302 may include the dual port RAMs 1316A to 1316C.

[0071]

According to the data communication method of the present invention, the external device outputs an access request for requesting the entire range of required data to the access request source data link unit, and then the entire range of data is transmitted to the access request source. Since other processing can be performed until the data link units are prepared, overhead can be reduced. Further, since the external device sequentially retrieves the entire range of data arranged in the access request source data link unit, the overall processing time can be reduced.

[Brief description of the drawings]

FIG. 1 is an essential part extracted diagram of a communication system for realizing a data communication method according to a first embodiment of the present invention.

FIG. 2 shows a dual port R used in the communication system of FIG.
It is an internal block diagram of AM.

FIG. 3 is a communication sequence diagram of the communication system of FIG. 1;

FIG. 4 is an operation flowchart of an external device of the communication system of FIG. 1;

FIG. 5 is an operation flowchart of a data processing unit of the access request source data link unit of the communication system of FIG. 1;

6 is an operation flowchart of a link processing unit of the access request source data link unit of the communication system of FIG. 1;

7 is an operation flowchart of a link processing unit of an access request destination data link unit of the communication system of FIG. 1;

8 is an operation flowchart of a data processing unit of an access request destination data link unit of the communication system of FIG. 1;

FIG. 9 is an essential part extracted diagram of a communication system for realizing a data communication method according to a second embodiment of the present invention.

FIG. 10 is an internal configuration diagram of a dual port RAM used in the communication system of FIG. 9;

FIG. 11 is a communication sequence diagram of the communication system of FIG. 9;

12 is an operation flowchart of a link processing unit of the access request source data link unit of the communication system of FIG. 9;

FIG. 13 is an essential part extracted diagram of a communication system for realizing a data communication method according to a third embodiment of the present invention.

14 is an internal configuration diagram of a dual port RAM used in the communication system of FIG.

FIG. 15 is a communication sequence diagram of the communication system of FIG. 13;

16 is an operation flowchart of a link processing unit of the access request source data link unit of the communication system of FIG. 13;

FIG. 17 is a diagram illustrating a main part of a communication system according to a conventional data communication method.

18 is an internal configuration diagram of a dual port RAM used in the communication system of FIG.

19 is a communication sequence diagram of the communication system of FIG.

20 is an operation flowchart of an external device of the communication system of FIG. 17;

21 is an operation flowchart of a data processing unit of the access request source data link unit of the communication system of FIG. 17;

FIG. 22 is an operation flowchart of a link processing unit of the access request source data link unit of the communication system of FIG. 17;

23 is an operation flowchart of a link processing unit of the access request destination data link unit of the communication system of FIG. 17;

24 is an operation flowchart of a data processing unit of an access request destination data link unit of the communication system of FIG. 17;

[Explanation of symbols]

100, 200, 300, 500 Communication systems 1301A, 1301B, 1301C Access requesting data link unit 1301K Access requesting data link unit 1302, 1302K Data processing unit 1303, 1303K Link processing unit 1318 Communication line 1319 Data line 1320, 1320K Access request Destination data link unit 1304A, 1304K External device 1316A, 1316B, 1316C, 1316K Dual port RAM 1401A, 1401K Request data buffer 1402A, 1402K Answer data buffer 61 Data storage degree area 111 Memory shortage notification area 1400 Information terminal

Claims (3)

(57) [Claims] 1. An external device connected via a data line.
Access request destination data via the
A link processing unit connected to the data link unit.
Wherein the access request source data link units
Issues an access request from an external device, the access request source data link unit is said response to the access request
Equipped with a data processing unit and a link processing unit via a communication line
A data communication method for sending a transmission request to an access request destination data link unit, receiving data from the access request destination data link unit, and passing the data to the external device, comprising: , The entire range of data required (the total amount of data>
An access request for requesting the amount of data that can be exchanged between the external device and the access request source data link unit at a time) is output. After the data of the entire range has been prepared, the data link units of the access request source are sequentially executed once at a time.
The access request source data link unit receives a data transmission request to the access request destination data link unit in response to the access request, and receives the data via the communication line. A data communication method, wherein when the data of the entire range is prepared, the data of the entire range is sequentially transferred to the external device by the data amount that can be exchanged at one time . 2. The data communication method according to claim 1, wherein the external device inquires of the access request source data link unit whether or not the entire range of data has been prepared, while executing other processing. A data communication method, wherein the access request source data link unit notifies a response as to whether data in the entire range has been prepared or a degree of data preparation. 3. The data communication method according to claim 1 or 2, wherein the access requesting data link unit transmits an external device to the external device when the data buffer becomes full before data in the entire range is prepared. A data buffer full, and in response to the data buffer full notification, the external device starts receiving data stored in the access request source data link unit up to that time. .