The original 1982 SynAssembler violated Atari's OS vector rules and utilized two "illegal" routines; a JSR E_GETCHR at $AB75 and a JSR E_OUTCHR at $B99A. Both Antic and Analog printed patch utilities which would replace the 800 address with the equivalent XL address resulting in two mutually incompatible versions.

SYNASM.FIX is the 800 version with an appended initialization routine, detailed in SYNFIX.DSM, to read the correct addresses for the machine at hand from the E: vector table at $E400 and poke them in the appropriate places; it sort of translates itself.

SynAssembler XL was apparently re-written and re-assembled as the areas around $AB75 and $B99A are different. I have not checked it thoroughly to find all of the changes nor verified that it is 800 compatible.

The sample files on the .ATR with .TXT extenders are not atascii files, but partially tokenized SynAssembler SAVEd source code and should be LOADed. The HELP.TXT file contains a good synopsis of the syntax.