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138 Siemens Simatic S7 Driver Online Help

When reading a STRING datablock, the following guidelines apply:

• You cannot split a STRING datablock over multiple TEXT blocks.

• Wide characters and UNICODE text are not supported.

• Add two bytes at the start of each STRING datablock. These bytes are needed

to store information about the string. For example, if you want to store a 10-

character piece of text, create a datablock that is 12 bytes long.

• The Text block you create to store STRING values cannot be greater than the

string in the datablock. For example, if you want to store a 10-character

string, create a Text block with a length of 10.

When writing text the driver does not pad zeroes at the end of the string.

STRING Data Type Examples

The length of the datablock is 8 bytes and the length of the associated Text block is 6 bytes.

The following text shows the values read and written by the SI7 driver.

Value Read by Driver... Text Read by iFIX...

Fred\0 Fred\0 (terminated with a null character)

Alarms Alarms

ABCDEFGHI\0 ABCDE\0

NOTE: Database Manager does not prompt you to add nonexistent datablocks referenced by

Text blocks.

Writing Text Examples

The length of the datablock is 12 bytes and the length of the associated Text block is 10 bytes.

The following text shows the values read and written by the SI7 driver.

Text Written by iFIX... Text Written to Hardware...

Fred Fred

1 2 ... 143 144 145 146 147 148 149 150 151 152 153 ... 267 268

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Siemens SIMATIC NET Spécifications Page 148