Quatech HSU-300 - Manual (Page 51)

Using configuration utilities Quatech Freedom USB-1/2/300 User’s Manual
This option is valid for baud rates in the range of 2400 bps to 115200
bps.
If this box is not checked, the software application is responsible for
manually switching RTS or DTR as needed.
Page 46 Rev 2.02 (2/24/2004)