I am using Open function for serial com,
it wouldn't open unless I open a terminal before which initiates the serial communication and then close it.
Looks like I miss HW setup here, but I don't know how to do it.
This is my code

comSettingStr = "COM4" & ":1200,N,8,1"
COMfile = FreeFile
Open comSettingStr For Binary Access Read Write As #COMfile Len = 140
Put #COMfile, , command
Application.Wait Now + #12:00:01 AM#
Get #COMfile, , response