PS/2 Library

The mikroC PRO for PIC32 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 :
`extern sfr atomic sbit PS2_Data;`	PS/2 Data line.	`sbit PS2_Data at RB0_bit;`
`extern sfr atomic sbit PS2_Clock;`	PS/2 Clock line.	`sbit PS2_Clock at RB1_bit;`
`extern sfr atomic sbit PS2_Data_Direction;`	Direction of the PS/2 Data pin.	`sbit PS2_Data_Direction at TRISB0_bit;`
`extern sfr atomic sbit PS2_Clock_Direction;`	Direction of the PS/2 Clock pin.	`sbit PS2_Clock_Direction at TRISB1_bit;`

Ps2_Config

Prototype	void 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 sbit PS2_Data at RB0_bit; sbit PS2_Clock at RB1_bit; sbit PS2_Data_Direction at TRISB0_bit; sbit PS2_Clock_Direction at TRISB1_bit; // End of PS2 pinout definition ... Ps2_Config(); // Init PS/2 Keyboard
Notes	None.

Ps2_Key_Read

Prototype	unsigned int Ps2_Key_Read(unsigned short value, unsigned short* special, unsigned short* *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.
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	unsigned short keydata = 0, special = 0, down = 0; ... // Press Enter to continue: do { if (Ps2_Key_Read(&keydata, &special, &down)) { if (down && (keydata == 16)) break; } } while (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.

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unsigned short keydata , special , down;
 
sbit PS2_Data            at RD0_bit;
sbit PS2_Clock           at RD1_bit;
sbit PS2_Data_Direction  at TRISD0_bit;
sbit PS2_Clock_Direction at TRISD1_bit;

void main() {

  CHECON = 0x32;
  AD1PCFG = 0xFFFF;                                   // Configure AN pins as digital I/O
  TRISD = 0;
  LATD = 0;
  
  UART1_Init(56000);                                  // Initialize UART module at 19200 bps

  Ps2_Config();                                       // Init 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
        //UART1_Write('\n');                          // uncomment this line if usart terminal also expects line feed
                                                      // for new line transition
      }
      else if (down && !special && keydata) {
        UART1_Write(keydata);                         // Send key to usart terminal
      }
    }
    Delay_ms(1);                                      // Debounce period
  } while (1);
}

HW Connection

Example PS2 keyboard connection

Example of PS2 keyboard connection

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