PS/2 (AT) Keyboard Module (Swordfish)

[gramo]

**broken link removed**
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):

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:

**broken link removed**

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

 

[3v0]

Cool.

Has me thinking of an application where I would use a keyboard.

 

[gramo]

Cheers 3v0,

At the cost of 4 pins to gain an interface to upwards of 101 keys, it goes a long was to make interaction with projects more accessible.

Almost everyone who's written a PIC program has relied at some-stage to use an array of switches or a matrix keypad for data entry. More often than not, I'd imagine the cost of the hardware, not to mention the I/Os required from the PIC would exceed that of what's required for a $5-10 keyboard.

If there's one more feature that might help cog application uses, perhaps its plug-and-play. There's no need to surrender a whole keyboard to one project - unplug it and use it on something else. The user module handles such scenarios quite well.

(caveat: hot swapping can potentially cause damage on older devices - we're talking fairly old there, newer Keyboards with PTC Fuses and robust port implementation will do fine)

 

[gramo]

That's a decent write-up on applications - I'll add it to the article