https://stackoverflow.com/questions/35912904/how-to-get-sqlsrv-on-xampp-working-with-medoo
instalas en xampp/php/ext la libreria y la declaras en el php inii
extension=sqlsrv_74_ts_x64
extension=pdo_sqlsrv_74_ts_x64
extension=pdo_odbc
luego tenes que instalar los drivers de odbc
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As you can see you need version 3.2 for PHP 5.6 support. I found download link and information about adding SQLSRV extension to php.ini for you.
https://www.microsoft.com/en-us/download/details.aspx?id=20098
https://msdn.microsoft.com/en-us/library/cc296203(v=sql.105).aspx
Finally you have to install Microsoft ODBC Driver 11 for SQL Server.