I don't
know if there's any Digital Research code in the TF20 OS, but it
wouldn't suprise me, BTW. It seems to be very similar to CP/M.
Here is track 0 from the disk image:
http://fjkraan.home.xs4all.nl/comp/tf20/tfdos_trk01.bin. It does contain
some BDOS like text: "Bdos Err On : $Bad Sector$Select$File R/O$"
Indeed.
As I said, I don;t know if there';s any DR code i nthere, but the OS
certainly seems very CP/M like. CP/M disk structute, etc. Given that the
TF20 is a Z80 +64K RAM + a boot ROM that is paged out after booting, it
wouldn't suprise me at all if the OS _was_ CP/M.
-tony