For new style RadioTrack cards only.
This function turns off the new-style RadioTrack cards. This function can also be used to mute the radio. The format of the function is:
return_data = RT2Off( rt_address )
The rt_address is the decimal value of the card's I/O location 780 (30C hex) or 524 (20C hex).
return_data returns the following values:
0 No errors.
1 Radio card can't be turned off.
10 TESTCFG.SYS could not be opened.