Acnodes PCH 3582 - Manual (Page 51)

outportb(0x4E, 0x07); //LDN selection register
3.10.4 Read/write GPIO sequence
1. Enter the extended function mode
2. Select logic device number
3. Read/write GPIO register value
4. Exit the extended function mode
3.10.5 Software programming example
Enter the extended function mode
Writing 87h to index address port twice will enter the extended function mode.
Example x86 assembly code:
mov dx, 4Eh
mov al, 87h
out dx, al
out dx, al
Example C code:
outportb(0x4E, 0x87);
outportb(0x4E, 0x87);
Exit the extended function mode
Writing AAh to index address port will exit the extended function mode.
Example x86 assembly code:
mov dx, 4Eh
mov al, 0AAh
out dx, al
Example C code:
outportb(0x4E, 0xAA);
Select logic device number
Example x86 assembly code:
mov dx, 4Eh
mov al, 007h ;LDN selection register
out dx, al
mov dx, 4Fh
mov al, 008h ;Select LDN=8, GPIO Port6
;or Select LDN9, GPIO Port2
out dx, al
Example C code: