How To Execute A Simple Stored Procedure

I'm executing simple stored procedure same to:

create procedure [dbo].[usp_procedure]@var1 int=null output,@var2 varchar(25)=null output,@var3 varchar(25)=null output,@var4 varchar(25)=null output,@var5 varchar(25)=null output,@action char(1)=null outputasbegin set nocoutn on;if @action = 'S'begin select * from t_table order by @var1end

in my script I call to this stored procedure but, this send me a error. my script is
$action="S";// Set up T-SQL query.$tsql = "call dbo.usp_T_Usuarios (@action=?)";// Assign parameter values.$params = array($action);// Specify types for parameters.$stmt = sqlsrv_query( $conn, $tsql, $params);echo "<br><br>Executed.....<br><br>";// Create and execute the statement. Display any errors that occur.if(!$stmt){ echo "Error executing the sp...<br>"; die( print_r( sqlsrv_errors(), true));}else{ echo "<br>Execute sp....<br><br>"; echo $stmt;}
and the error is:

conected...The conection was succefully.Executed.....Error executing the sp...Array ( [0] => Array ( [0] => 07009 [SQLSTATE] => 07009 [1] => 0 [code] => 0 [2] => [Microsoft][SQL Native Client]�ndice descriptor no válido [message] => [Microsoft][SQL Native Client]�ndice descriptor no válido ) [1] => Array ( [0] => 07009 [SQLSTATE] => 07009 [1] => 0 [code] => 0 [2] => [Microsoft][SQL Native Client]Número de parámetros no válido [message] => [Microsoft][SQL Native Client]Número de parámetros no válido ) )I need help me. some body tell me what is my error. please.