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PS/2 (AT) Keyboard Module (Swordfish) 2010-10-03


I recently wrote a Swordfish module which simplifies the process of interfacing with a PS2 Keyboard.

Here's an example of the module in use. Note that its as simple as calling the function "swKBD.NewKey". From there, if a key has been pressed, it is extracted and stored in the registers KBD.KeyChar and KBD.KeyCode (KeyChar contains the converted ASCII character while KeyCode contains the raw scan key code):
Code:
Device = 18F2520                            // 18F2520 PIC in use, could be any 18F PIC
Clock = 32                                  // clock speed is 32Mhz (8MIPS)
Config MCLRE = Off                          // disable MCLR
 
Include "InternalOscillator.bas"            // search for "User Module Pack" at www.digital-diy.com
Include "USART.bas"                         // used for displaying content on a uart terminal
Include "swKBD.bas"                         // PS2 Keyboard module. URL http://digital-diy.com/home/swordfish/user-modules/242-ps2-keyboard-module-swkbdbas.html
 
SetBaudrate(br38400)                        // initialise USART for 38400 baud
USART.Write("Power On",13,10)               // send a message to the terminal
 
While True                                  // main program loop
    If swKBD.NewKey Then                    // checks the device for new information
        If KBD.ValidChar Then               // ensure the key is a valid non-white space character
            USART.Write(KBD.KeyChar)        // yes, display it via USART
        ElseIf KBD.KeyCode = KBD_ENTER Then // check if the 'Enter' key was pressed
            USART.Write(13,10)              // yes, send a line feed and carriage return
        EndIf                               //
    EndIf                                   //
 
    High(PORTB.7)                           // toggle PORTB.7 high then low,
    Low(PORTB.7)                            // to measure the time it takes between loops
Wend                                        //
The keyboard will buffer upto 16 key presses which allows for the PIC to go and perform other tasks. Each call to swKBD.NewKey will take a maximum of 4mS to complete (in the above example, the secondary task is to toggle PORTB.5 - which occurs at 250Hz).

A handy feature that was recently added detects if the keyboard has been unplugged, and will automatically re-configure the keyboard when it is reconnected.

Thanks to the PORTB pull-up trick, you get upwards of 101 keys at the cost of 4 wires like so:



You can find the latest version of the module in the article: PS/2 Keyboard Module (swKBD.bas) (along with detailed usage/tips)

Comments welcome
Author
gramo
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