Intel H310 Technical Manual page 16

Pin 1&2 of AT_COPEN (4-pin): AT Mode Select
AT_COPEN
*ATX Mode Selected: Press power button to power on after power input ready;
AT Mode Selected: Directly power on as power input ready.
Pin 3&4 of AT_COPEN (4-pin): Case Open Message Display Function Select
AT_COPEN
Pin (3&4) short: When Case open function pin short to GND, the Case open function
was detected. When used, needs to enter BIOS and enable 'Case Open Detect'
function. In this case if your case is removed, next time when you restart your computer,
a message will be displayed on screen to inform you of this.
Pin 1&2 of AT_COPEN
→ AT Mode Select
Pin1
1-2 Open: ATX Mode
Selected(Default);
;
Pin1
1-2 Closed: AT Mode Selected.
Pin 3&4 of AT_COPEN
→ Case Open Detection
Pin1
11
4
4
4