Did you check php.ini ?
Thanks for the reply. It is set to 4096, so I don't think that's the problem.
I tested it on ODBC driver 13.00.12.00 / PHP Version 5.3.27 / Win7 and got more than 256 chars.
You can test ODBC DSN and driver without PHP (import records by FM for example) for narrowing the problem.
Reloaded PHP. Restarted Apache. Everything is fine.
Go figure. dll, bad ini entry? Ah well. Problem solved.
Thanks for the responses.