PS/2 Library

The mikroBasic PRO for dsPIC30/33 and PIC24 provides a library for communication with the common PS/2 keyboard.

Important :

The library does not utilize interrupts for data retrieval, and requires the oscillator clock to be at least 6MHz.
The pins to which a PS/2 keyboard is attached should be connected to the pull-up resistors.
Although PS/2 is a two-way communication bus, this library does not provide MCU-to-keyboard communication; e.g. pressing the Caps Lock key will not turn on the Caps Lock LED.

External dependencies of PS/2 Library

The following variables must be defined in all projects using PS/2 Library:	Description :	Example :
`dim PS2_Data as sbit sfr external`	PS/2 Data line.	`dim PS2_Data as sbit at RB0_bit`
`dim PS2_Clock as sbit sfr external`	PS/2 Clock line.	`dim PS2_Clock as sbit at RB1_bit`
`dim PS2_Data_Direction as sbit sfr external`	Direction of the PS/2 Data pin.	`dim PS2_Data_Direction as sbit at TRISB0_bit`
`dim PS2_Clock_Direction as sbit sfr external`	Direction of the PS/2 Clock pin.	`dim PS2_Clock_Direction as sbit at TRISB1_bit`

Ps2_Config

Prototype	sub procedure Ps2_Config()
Description	Initializes the MCU for work with the PS/2 keyboard.
Parameters	None.
Returns	Nothing.
Requires	Global variables : `PS2_Data:` Data signal line `PS2_Clock:` Clock signal line `PS2_Data_Direction:` Direction of the Data pin `PS2_Clock_Direction:` Direction of the Clock pin must be defined before using this function.
Example	' PS2 pinout definition dim PS2_Data as sbit at RB0_bit dim PS2_Clock as sbit at RB1_bit dim PS2_Data_Direction as sbit at TRISB0_bit dim PS2_Clock_Direction as sbit at TRISB1_bit ' End of PS2 pinout definition ... Ps2_Config() ' Init PS/2 Keyboard
Notes	None.

Ps2_Key_Read

Prototype	sub function Ps2_Key_Read(dim byref value as byte, dim byref special as byte, dim byref pressed as byte) as word
Description	The function retrieves information on key pressed.
Parameters	`value:` holds the value of the key pressed. For characters, numerals, punctuation marks, and space `value` will store the appropriate ASCII code. Routine “recognizes” the function of `Shift` and `Caps Lock`, and behaves appropriately. For special function keys see Special Function Keys Table. `special:` is a flag for special function keys (`F1`, `Enter`, `Esc`, etc). If key pressed is one of these, `special` will be set to 1, otherwise 0. `pressed:` is set to 1 if the key is pressed, and 0 if it is released.
Returns	`1` if reading of a key from the keyboard was successful `0` if no key was pressed
Requires	PS/2 keyboard needs to be initialized. See Ps2_Config routine.
Example	dim value, special, pressed as word ... ' Press Enter to continue: do { if (Ps2_Key_Read(value, special, pressed)) then if ((value = 13) and (special = 1)) then break end if end if loop until (0=1)
Notes	None.

Special Function Keys

Key	Value returned
F1	1
F2	2
F3	3
F4	4
F5	5
F6	6
F7	7
F8	8
F9	9
F10	10
F11	11
F12	12
Enter	13
Page Up	14
Page Down	15
Backspace	16
Insert	17
Delete	18
Windows	19
Ctrl	20
Shift	21
Alt	22
Print Screen	23
Pause	24
Caps Lock	25
End	26
Home	27
Scroll Lock	28
Num Lock	29
Left Arrow	30
Right Arrow	31
Up Arrow	32
Down Arrow	33
Escape	34
Tab	35

Library Example

This simple example reads values of the pressed keys on the PS/2 keyboard and sends them via UART.

Copy Code To Clipboard

program PS2_Example

dim keydata, special, down as byte

dim PS2_Data            as sbit at RB0_bit
    PS2_Clock           as sbit at RB1_bit
    PS2_Data_Direction  as sbit at TRISB0_bit
    PS2_Clock_Direction as sbit at TRISB1_bit

main:
  ADPCFG = 0xFFFF            ' Configure AN pins as digital I/O

  UART1_Init(19200)           ' Initialize UART module at 19200 bps


  Ps2_Config()                ' Init PS/2 Keyboard
  Delay_ms(100)               ' Wait for keyboard to finish
  UART1_Write_Text("Ready")   ' Ready
  UART1_Write(13)             ' Line Feed
  UART1_Write(10)             ' Carriage return


  while TRUE                                          ' Endless loop
    if Ps2_Key_Read(keydata, special, down) then      ' If data was read from PS/2
      if (down <> 0) and (keydata = 16) then          ' Backspace read
        UART1_Write(0x08)                             ' Send Backspace to usart terminal
      else
        if (down <> 0) and (keydata = 13) then        ' Enter read
          UART1_Write(10)                             ' Send carriage return to usart terminal
          UART1_Write(13)                             ' Uncomment this line if usart terminal also expects line feed
                                                      '   for new line transition
        else
          if (down <> 0) and (special = 0) and (keydata <> 0) then   ' Common key read
            UART1_Write(keydata)                      ' Send key to usart terminal
          end if
        end if
      end if
    end if
    Delay_ms(10)                                      ' Debounce period
  wend
end.

HW Connection

Example PS2 keyboard connection

Example of PS2 keyboard connection

Want more examples and libraries?
Find them on