Firmware of a BTX decoder mark I, part number 325221-02, checksum $3E0F. This was copied from a 27128 EPROM labelled with the part number and "BTX C64 C128".
Firmware of a BTX decoder mark II, dumped from a 27256 EPROM. The sticker on the erase window has a Siemens logo and "V30113-" at the top line, "C375-81-1" at the middle line and "( EX )" at bottom. The checksum is $D68F.