HP dc71xx Manuel D’Utilisation

When the system is turned on, the keyboard processor generates a Power-On Reset (POR) signal 
after a period of 150 ms to 2 seconds. The keyboard undergoes a Basic Assurance Test (BAT)  
that checks for shorted keys and basic operation of the keyboard processor. The BAT takes from 
300 to 500 ms to complete. 

If the keyboard fails the BAT, an error code is sent to the CPU and the keyboard is disabled until 
an input command is received. After successful completion of the POR and BAT, a completion 
code (AAh) is sent to the CPU and the scanning process begins. 

The keyboard processor includes a 16-byte FIFO buffer for holding scan codes until the system is 
ready to receive them. Response and typematic codes are not buffered. If the buffer is full (16 
bytes held) a 17th byte of a successive scan code results in an overrun condition and the overrun 
code replaces the scan code byte and any additional scan code data (and the respective key 
strokes) are lost. Multi-byte sequences must fit entirely into the buffer before the respective 
keystroke can be registered.    

Keyboard  
Interface 
(System Unit)

 

Data/ 

CLK

 

Num 
Lock

Caps

Lock

Scroll 

Lock

 
 

Keyboard 

Processor

 

Matrix

Drivers

 

Matrix 

Receivers

 

 

Keyswitch 

Matrix