I seem to remember having to send three consecutive
software reset
commands to something or other, quite possibly 6850:s, and probably
Motorola ones. If you sent only one, the chip did not reset, you had to
send three at once.
That sounds more like the Intel 8251 USART. IIRC on that chip you have to
send the reset command 3 times to ensure it's treated as a command and
not as data to be loadrd into one of the configuration registers.
-tony