Use the search feature to view Kepware's repository of more than 500 Knowledge Base articles. Narrow your results or type your query into the search field below.

Alternatively, if you are unable to find a solution, we have an additional resource - our PTC eSupport Portal . If you are prompted to log into the eSupport Portal, you can use your My Kepware credentials. Need a My Kepware account? Create one here .

Search Solution Results By:
View All Solutions

Kepware Knowledge Base: Solution

The Server Returns a String from the S7-1200 PLC with the First Two Characters Missing

Last Update: 11/7/2018

The first two characters are missing when reading a string from a data block in a Siemens S7-1200 PLC.

Possible Cause:
A string that is created in a data block in the S7-1200 PLC will have a fixed length of 256 bytes. Its first two bytes tell the length of the current string data and the maximum length of the string. In order to be a specific length in a PLC data block, the string must be created as an array of characters. In both types of data blocks, the end of the string will be marked with a null terminator. If a tag is created as a string in the server, the driver will always treat the first two bytes as the length fields. As a result, it will not read them. For example, an array of 18 characters is created in "DB 12" and is initialized to the value of "KEPWARE". If a tag is then created in the server with an address of "DB12,STRING0,18" a value of "PWARE" will be displayed in the client. This is because the driver assumes that the first two bytes are length data. If a tag is created in the server with an address of "DB12,C0,18" and the data type is set to string, the entire string will be displayed as a value in the client.

When reading true strings from a data block, use the String address type. Alternatively, use the character address types to ensure that the leading characters are not ignored.