'/////////////////////////////////////////
'   pckeyb2.bas
'
'   - Processor Atmel AT 89C52
'   - Implementation of the PC keyboard
'   - Listing of scan codes to serial port
'   - Crystal is 11.059 MHz,
'   J. Nahtigal,  ver 1.2       3/2000
'////////////////////////////////////////

'directives
$crystal = 11059000
$baud = 9600
'labels
Clockline Alias P3.3
Dataline Alias P3.6




'global variables
Dim Breakcode_flag As Byte
Dim Key_code As Byte
Dim Key_pressed_flag As Byte , A As Byte

'..... start of the main program .......
On Int1 Ext_interrupt1
Enable Int1
Enable Interrupts

'control listing
Print " pckeyb2 "


 'program main loop
Key_pressed_flag = 0
Breakcode_flag = 0
Do
  '
  'user program storage
  '
  '
Loop
'..... end of main program .........





'.......................................
Ext_interrupt1:
   Disable Int1

   'bit1 is start bit
   Call Wait_for_high

   'read databits from 0 to 7
   For A = 1 To 8
       Call Wait_for_low
       $obj A2b6                        'mov c,dataline 
       Rotate Key_code , Right
       Call Wait_for_high
   Next

   'read Parity bit
   Call Wait_for_low
   Call Wait_for_high

   'read Stop bit
   Call Wait_for_low
   Call Wait_for_high


   'verify Key_code and Breakcode_flag
   'if Key_code equals E0h = 224
   If Key_code = 224 Then
         Goto Exit_routine_ext1
   End If


   If Breakcode_flag = 1 Then
         Breakcode_flag = 0
         Goto Exit_routine_ext1
   End If

   'if Key_code equals F0h = 240
   If Key_code = 240 Then
         Breakcode_flag = 1
         Goto Exit_routine_ext1
   End If


   'Key_code = OK
   'mark the flag, new key pressed
   'and display key_code to serial port
   Key_pressed_flag = 1
   Printhex Key_code

Exit_routine_ext1:
   Enable Int1

Return
'.......................................


Sub Wait_for_high
   Bitwait Clockline , Set
End Sub


Sub Wait_for_low
   Bitwait Clockline , Reset
End Sub
'.......................................