Machine Characteristics - KBC Output Port
Table of Contents

This is one of a number of machine-characteristics.

KBC Output Port

This table shows the initial values read using command 0xd0 from the keyboard controller's output port.

Machine KBC Output Port
Dell Latitude XP 475D laptop. 80486 75MHz. Phoenix BIOS 1.10 1100_1000
ABIT AB-SM5-A. Pentium MMX 233MHz. Award Modular BIOS v4.51PG 0100_1001
AOpen motherboard. Pentium 3 600MHz. Award BIOS 3.60 0100_1001
Viglen MPC-L. Geode 399MHz. ION A503 BIOS 0100_1011
Asus EEE 4G netbook. Celeron M ULV 630MHz. AMI ASUS 701 BIOS 1100_1111
Gateway laptop. Dual-core Core 2 T5300 1.7GHz. Phoenix BIOS 0100_1001
Asus M2NPV-VM. Athlon X2 Dual-core 2.3GHz. Phoenix BIOS 1201 0000_0001
Jetway NC91. Dual-core Atom 1.6GHz. Phoenix-AwardBIOS xxxx_xxxx


  • The bits are
    • 7 - data out to the keyboard
    • 6 - clock out to the keyboard
    • 5 - IRQ12 output (PS/2) or input buffer empty signal (pre-PS/2)
    • 4 - IRQ1 output
    • 3 - clock out to the mouse
    • 2 - data out to the mouse
    • 1 - output to A20 gate (set to 1 to enable A20)
    • 0 - system reset output (set to 0 to reset the machine)
  • In all machines which responded the two interrupt outputs read as 0.
  • Both clock outputs (to keyboard and mouse) in most cases read as 1.
  • The system reset output does not always read as 1. Writing this bit back as read could hang or reset the machine.
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