JPH0514365A - Scan transmission system - Google Patents

Abstract

PURPOSE:To reduce the burden of stations and a network to efficiently transmit data by sending stored data only at the time of the change of a specific bit due to rewrite of stored data. CONSTITUTION:If data in a scan memory 13 where data from a CPU 4 is stored is changed by rewrite or the like, a block 12 data change bit DVB is given. A CPU 12 detects this change, and data is set and sent from a LAN interface 14 to a network 2. If data is not changed, the CPU 12 instructs the LAN interface 14 to pass the token from the network 2, and data is not sent. Since the processing to pass the token is performed when data is not changed, the burden of the CPU 12 and the network 2 is reduced and the wait time of the other stations is shortened to effectively use the LAN.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scan transmission system for highly efficient scan transmission in a local area network (LAN).

[0002]

2. Description of the Related Art In a LAN, when transferring data between a plurality of stations connected to a network, there is a scan transmission method as one of the methods, which is a network. One token (identifier) signal is circulated on the upper side, and when the token arrives, a transmission right is given so that the data is transmitted cyclically. That is, upon receiving a token, the station obtains the transmission right, reads the data from the memory in the station at a predetermined timing, and transfers the data to another station. As a result, the data transmitted by another station can be read.

Regarding this type of transmission system, for example, Japanese Patent Laid-Open Nos. 62-117431 and 61-285846,
JP-A-58-202692 and JP-A-2-119451
and so on. For example, in the case of Japanese Patent Laid-Open No. 62-117431, when data is transmitted between a slave station and a center, the previous data and the current data are compared, and if a change is recognized, the synchronous data Instead of this, data is transmitted, and if there is no change, a synchronous word is always transmitted.

[0004]

However, in the above-mentioned prior art, even if there is no change in the data, all the data are periodically refreshed and these data are transmitted. As a result, the load on the CPU in the station and the communication load on the network increase, resulting in inefficient operation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scan transmission system which reduces the burden on the station and the network and enables efficient data transmission.

[0006]

To achieve the above object, the present invention provides a scan transmission system for cyclically transmitting data from a station to a network by a token passing system. First means for assigning a specific bit to each block of stored data in the memory provided in the station; and when the specific bit indicates a change in the stored data, the data is stored. The network
Second means for transmitting data to the network when the specific bit indicates that the stored data has not changed.

[0007]

According to the above means, the specific bit is stored in the storage data.
Data is stored only when the data changes due to rewriting.
Data from the station to the network and store
If there is no change in the data, no data is sent to the network. This reduces the burden on the CPU and network in the station and enables efficient data transmission.

[0008]

1 is a block diagram showing a scan transmission system according to the present invention.

LAN station 1 for network 2
, A system bus 3 is connected to the LAN station 1, and the factory station (F
A) A control unit (CPU) 4 such as a computer of the system or a computer for performing processing in each department is connected. The LAN station 1 stores a CPU 12 that executes various controls for the internal bus 11, the network 2 or the system bus 3, data to be transmitted or data transferred from the network 2. The scan memory 13 and the LAN interface (LAN I / F) 14 for controlling the exchange of data to and from the network 2 are provided. For the scan memory 13, for example, a dual port memory is used.

In the present invention, as shown in FIG. 2, each of the blocks 5a to 5c of the transmission buffer is provided with a data change bit DVB which is a specific bit. This data change bit DVB is flagged when each of blocks 5a-5c is rewritten. Data change bit DVB
Is allocated at least 1 bit, which is
It can be provided as a software or software.

Next, the operation of the embodiment having the above configuration will be described.

Data from the CPU 4 is stored in the scan memory 13, but when a change occurs in the data due to rewriting or the like, the block is read by the CPU.
The data change bit DVB is set by 4 (0 → 1)
It This change in data content is detected by the CPU 12, and based on this detection, the CPU 12 issues an exchange command to change the data change bit DVB (1 → 0), and at the same time, immediately transmits the data. LAN interface
A command is output to the face 14 to set and send the data.

On the other hand, the network 2 periodically receives a
The LAN interface 14 receiving this token forms a queue and sends the data read from the scan memory 13 to the network 2 in accordance with the queue. In addition, the scan memory 13
If there is no change in the data inside, the data change bit D
VB does not change. In this case, the CPU 12 which regularly detects the presence or absence of change determines that there is no change in data, and passes the token from the network 2 to the LAN interface 14. Give instructions to do so. Therefore, the LAN interface 14 does not form a queue, and no data is sent from the LAN station 1 side to the network 2. By the process of passing the token in this way, the burden on the CPU 12 and the network 2
Since the communication load on the LAN can be reduced and the waiting time in other stations can be shortened, the LAN can be effectively used.

Incidentally, in the conventional scan transmission system, even if there is no change in the data, the station data is periodically refreshed and sent to the network. The CPU 12 takes a lot of time for this processing, and since the data which does not need to be transmitted is run on the network, the burden on the network is heavy.

[0015]

As described above, the present invention is provided in the station in the scan transmission system for cyclically transmitting data from the station to the network by the token passing system. First means for assigning a specific bit to each block of stored data in the memory; and sending the data to the network when the specific bit indicates a change in the stored data. The second means for not sending data to the network when the specific bit indicates that the stored data has not changed is provided, so that the burden on the CPU in the station and the network can be improved.
This reduces the burden on the clock and enables efficient data transmission.

[Brief description of drawings]

FIG. 1 is a block diagram showing a scan transmission method according to the present invention.

FIG. 2 is a conceptual diagram illustrating setting of a data change bit DVB according to the present invention.

[Explanation of symbols]

 1 LAN station 2 Network 3 System bus 4 CPU 5a-5c block DVB data change bit

Claims (1)

Claim: What is claimed is: 1. In a scan transmission system for cyclically transmitting data from a station to a network by a token passing system, a memory provided in the station is provided. First means for assigning a specific bit to each block of stored data; and sending the data to the network when the specific bit indicates a change in the stored data, the specific bit Means for not transmitting the data to the network when the storage data has not changed, the scan transmission method.