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212 Siemens Simatic S7 Driver Online Help

You should periodically start the I/O Driver Tool, examine the driver configuration

datablock address properties, and modify them for optimization.

Example

The following example assumes that the selected memory type has a limit of 238 bytes per

datablock, and the SI7 driver configuration has not been loaded.

[1] Create a tag referencing address M230.

Once this tag is added, the driver configuration has a datablock (we will call it

DataBlock1 in this example) with a start address of M230, an end address of M230,

and a length of 1.

[2] Create a tag referencing address M5.

When this tag is added, the driver configuration has another datablock (we will call it

DataBlock2 in this example) with a start address of M5, end address of M5, and a

length of 1.

[3] Create a tag referencing address M220.

When this tag is added, DataBlock2 in the driver configuration starts at register M5,

ends at register M220, and has a length of 216.

This method of extending the datablock may not have a major impact on small

configurations. However, for large configurations, it is more efficient to extend

DataBlock1 to start at M220 and end at M230 and change DataBlock2 to start at M5 and

end at M5 because the first scenario generates the following messages:

• Message 1: M5, length 216

• Message 2: M230, length 1

The second scenario, by comparison, generates these messages:

• Message 1: M5, length 1

• Message 2: M220, length 11

In both cases, the same three registers of data are polled. However, by requesting smaller

groups of contiguous data, as in the second scenario, the driver configuration uses less

bandwidth.

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Siemens SIMATIC NET Spécifications Page 222