The following figures show bit definitions for the input, output, and test-input ports.
(A) Input Port Definitions
BIT
FUNCTION
0
Undefined
1
Undefined
2
Undefined
3
Undefined
4
RAM on System Board
0: Disable 2nd 256 KB of System Board RAM
1: Enable 2nd 256 KB of System Board RAM
5
Manufacturing Jumper Installed
0: Manufacturing Jumper
1: Jumper Not Installed
6
Display Type Switch
0: Primary Display Attached to Color/graphics
0: Primary Display Attached to Monochrome
7
Keyboard Inhibit Switch
0: Keyboard Inhibited
1: Keyboard Not Inhibited
(B) Output Port Definitions
BIT
FUNCTION
0
System Reset
1
Gate A20
2
Undefined
3
Undefined
4
Output Buffer Full
5
Input Buffer Empty
6
Keyboard Clock (Output)
7
Keyboard Data (Output)
(C) Test-Input Definitions
BIT
FUNCTION
0
Keyboard Clock (Input)
1
Keyboard Data (Input)
11