It's been a while since I used the Buffalo monitor on an 'HC11 but my recollection was that all it needed was a terminal program. With Visa connecting to the PC serial port you should be able to do something like:
1) Setup Visa port com2, 9600, etc.
2) Send , pause
3) If no buffalo prompt, loop to 2)
4) Send string 'mm 102b', wait for '>'
5) Send string '35'
6) Close Visa session
7) Setup Visa port com2, 300, etc.
😎 Send , pause
9) If no buffalo prompt, loop to 😎
10) Send string 'load t'
11) **** Tricky part: I don't remember if the Buffalo monitor wants to use something like xmodem or zmodem for the download protocol; if so, you will have to find or write something compatible to do the actual file transfer, or write a l
ittle hack to read the .s19 file and poke it with the 'mm xx' command (probably easier).
12) Check for 'done', close Visa.
There is a little hand waving in the above, but the general approach should work just fine.
Matt