post4dPCI POST Code Display POST4D During the Power On Self-Test (POST), most PC BIOS write diagnostic codes to port 80h or 84 (jumper selection). Use POST4D to display these codes on5V PCI interface (not compatible with ALIX.1C ALIX.1D). During power on self-test (POST), most PC BIOSes will write diagnostic codes to port 80h or port 84h (jumper selection). Use post4d