Brother MFC 8840D - Manual (Page 166)

APPENDIX A - 7
ftp> quit
When you see 226 Data Transfer OK/Entering
FirmWareUpdate mode , you can be sure that the firmware file is
being transferred to the Print/Fax server. If you do not see this
message, the file you are sending to the printer will either be ignored
or the printer will print garbage.
You must use the “bin” command to put the FTP client into
Binary communications mode. If you do not specify the bin
command the upgrade process will not function correctly.