PHP,SQL Server:在存储过程中使用二进制数据

我有一个如下所示的存储过程:

CREATE PROCEDURE [dbo].[StoreThing]
    @pid int = 0,
    @data binary(236) = NULL,
AS
BEGIN
    INSERT INTO thingTable (pid, data) VALUES (@pid, @data)
END

(大大简化了,但那不是重点)

我试图从PHP脚本调用此过程,如下所示:

function storeThing($pid, $data) {
    global $dbconn;

    if(strlen($data) != 236) return false;

    $proc = mssql_init('StoreThing', $dbconn);

    mssql_bind($proc, '@pid', $pid, SQLINT4);
    mssql_bind($proc, '@data', $data, SQLCHAR, false, false, 236);

    $result = mssql_execute($proc);
    if(!$result) die(mssql_get_last_message());

    return true;
}

Warning: mssql_execute() [function.mssql-execute]: message: Implicit conversion from data type char to binary is not allowed. Use the CONVERT function to run this query. (severity 16)

显然,问题是 SQLCHAR 为数据字段设置类型I。但是,由于没有SQLBINARY常量,我不确定将其设置为什么。