Just managed to compile my first 7800 source! ;-)
If you're using Dans 7800 devkit and Textpad, you might want to change make.bat a little:
dasm %1.s -f3 -v3 -o%1.bin -llist.txt 78hdr %1.bin %1.a78 0000 a78sign -f %1.a78
Now you can assign a new "Extra" to Textpad with the commandline
and you can have a new binary compiled straight from Textpad.