Scanning FNC1 with GS1-128, EAN-128, UCC-128Link

When I create a barcode with or without the FNC1, the scanner returns a precisely identical character string back. In this character string my software cannot recognize where the end of a variable data length is. Can you help?
To get the control character FNC1 of the scanner transmitted, the scanner must this support this functionality. The FNC1 ordinarily has only internal meaning in the Code 128 (which is the base of the EAN128) and will not transmit correctly. The scanner must offer the option, to transmit the FNC1 in EAN-128.