PDO with MS SQL Server - output parameters/return values not returned

I am unable to get the values of output parameters for SQL Server stored procedures that have multiple parameters or return values for any procedures. I have tried this with both the odbc: and mssql: drivers on a Windows XP development machine. (The live application will be hosted on a Windows server.) Examples 1715 and 1716 on the PHP manual page http://www.php.net/manual/en/ref.pdo.php) demonstrate calling stored procedures with output parameters. I ran these and 1716 worked. Example 1715 worked if I changed the 3rd parameter (data type) to the same as used in 1716. However, when I added a second parameter to either of them, they stopped returning values to the bound variables. I am trying to get this to work with PDO instead of the MSSQL library since that seems to be the direction PHP is heading now that MS has dropped support for DB-LIB. (The same stored procedures work when I call them using the MSSQL functions.) Is there a different driver I should try, or are there connection options that need to be set?