Saving TMemo field data to a Blob field (Interbase Table) via SQL Update Query

Can anyone tell me how to update a Blob field in a Interbase table using a Sql
update command updating it with data from a TMemo field eg.
I'am having problems defining the Params line.

SQL.Add('Update aTable');
SQL.Add('SET aBlob = :Tmemodata');
Prepare;
Params[0].AsString := aMemo.Lines;

Can anybody help.

Thanks

David Lee.