PS/2 Library

The mikroC PRO for 8051 provides a library for communication with the common PS/2 keyboard.

Notes:

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 :
`extern sfr sbit bdata PS2_DATA;`	PS/2 Data line.	`sbit PS2_DATA at P0_0_bit;`
`extern sfr sbit bdata PS2_CLOCK;`	PS/2 Clock line.	`sbit PS2_CLOCK at P0_1_bit;`

Ps2_Config

Prototype	void Ps2_Config();
Returns	Nothing.
Description	Initializes the MCU for work with the PS/2 keyboard.
Requires	Global variables : `PS2_DATA:` Data signal pin `PS2_CLOCK:` Clock signal pin must be defined before using this function.
Example	// PS2 pinout definition sbit PS2_DATA at P0_0_bit; sbit PS2_CLOCK at P0_1_bit; ... Ps2_Config(); // Init PS/2 Keyboard

Ps2_Key_Read

Prototype	unsigned short Ps2_Key_Read(unsigned short value, unsigned short* special, unsigned short* *pressed);
Returns	`1` if reading of a key from the keyboard was successful `0` if no key was pressed
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.
Requires	PS/2 keyboard needs to be initialized. See Ps2_Config routine.
Example	unsigned short value, special, pressed; ... // Press Enter to continue: do { if (Ps2_Key_Read(&value, &special, &pressed)) { if ((value == 13) && (special == 1)) break; } } while (1);

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.

unsigned short keydata = 0, special = 0, down = 0;
 
// PS2 module connections
sbit PS2_DATA  at P0_0_bit;
sbit PS2_CLOCK at P0_1_bit;
// End PS2 module connections

void main() {

  UART1_Init(4800);         // Initialize UART module at 4800 bps
  Ps2_Config();             // Initialize PS/2 Keyboard
  Delay_ms(100);            // Wait for keyboard to finish
  
  UART1_Write_Text("Ready");
  UART1_Write(10);          // Line Feed
  UART1_Write(13);          // Carriage return

  do {
    if (Ps2_Key_Read(&keydata, &special, &down)) {
      if (down && (keydata == 16)) {// Backspace
         UART1_Write(0x08);
      }
      else if (down && (keydata == 13)) {// Enter
        UART1_Write('r');               // send carriage return to usart terminal
        //Usart_Write('n');             // uncomment this line if usart terminal also expects line feed
                                         // for new line transition
      }
      else if (down && !special && keydata) {
        UART1_Write(keydata);
      }
    }
    Delay_ms(10);            // debounce
  } while (1);
}

HW Connection

Example PS2 keyboard connection

Example of PS2 keyboard connection

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