IBSQL2.ParamByName('Data').AsBytes := LData;
........
procedure TIBXSQLVAR.SetAsBytes(const Value: TBytes);
var
  ss : TBytesStream;
begin
  if (FXSQLVAR.SqlDef = SQL_BLOB) then
  begin
    ss := TBytesStream.Create(Value);
    try
      LoadFromStream(ss);
    finally
      ss.Free;
    end;
  end
  else
    AsString := StringOf(Value);
end;

function StringOf(const Bytes: TBytes): UnicodeString;
begin
  if Assigned(Bytes) then
    Result := TEncoding.Default.GetString(Bytes, Low(Bytes), High(Bytes) + 1)
  else
    Result := '';
end;

procedure TIBXSQLVAR.SetAsString(const Value: String);
begin
  SetAsCPString(Value, FSQL.Database.CharacterSetCodePage); // AnsiString
end;

procedure TIBXSQLVAR.SetAsCPString(const Value: String; CodePage : Integer);
begin
  ........
  if (stype = SQL_TEXT) or (stype = SQL_VARYING) then
  begin
    if CodePage <> 0 then
    begin
      Encoding := TMBCSEncoding.Create(CodePage);
      try
        bt := Encoding.GetBytes(Value);
        SetStringValue;
      finally
        Encoding.Free;
      end;
    end
end;