Writing Special Variables - Siemens SIMATIC S7-1200 System Manual

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12.7 User-defined Web pages

Example: Reading a special variable with a Use clause

In this example, the HTTP special variable "HEADER:Status" receives the value of the PLC

tag "Status".

Writing special variables

The Web server provides the ability to write values to the CPU from special variables in the

HTTP request header. For example, you can store information in STEP 7 about the cookie

associated with a user-defined Web page, the user that is accessing a page, or header

information. The Web server provides access to specific special variables that you can write

to the CPU when logged in as a user with privileges to modify variables.

The type of special variable and is one of the following:

COOKIE_VALUE

Specific variable within the types defined above, as shown in these examples:

HEADER:Accept: content types that are acceptable

HEADER:User-Agent: information about the user agent originating the request.

SERVER:current_user_id: id of the current user; 0 if no user logged in

SERVER:current_user_name: name of the current user

COOKIE_VALUE:<name>: value of the named cookie

Enclose the Name clause in single quotation marks.

If no Use clause is specified, the special variable name corresponds to a PLC vari-

able name. Enclose the complete Name clause within single quotation marks and

the PLC tag in double quotation marks. The special variable name must match the

PLC tag name exactly.

Refer to HTTP documentation for a list of all the names of HEADER variables.

The variable name in your STEP 7 program into which you want to write the special

variable, which can be a PLC tag name, or a data block tag.

The Varname must be enclosed in single quotation marks. Within the single

quotes, use double quotation marks around a PLC tag or data block name. The

data block name is within the double quotes but not the data block tag name. Note

that for data block tags, you use the name of the block and not a data block num-

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK