HOME       UP       PREV       FURTHER NOTES       NEXT (Counters and Timers)  

Keyboard Controller (scan multiplexed type).

  output [3:0] scankey;
  input pressed;
  reg int_enable, pending;
  reg [3:0] scankey, pkey;

  always @(posedge clk) begin
     if (!pressed) pkey <= scankey;
     else scankey <= scankey + 1;
     
     if (hwen) int_enable <= wdata[0]
     pressed1 <= pressed;
     if (!pressed1 && pressed) pending <= 1;
     if (hren) pending <= 0;
     end
  assign interrupt = pending && int_enable;
  assign rdata = { 28'b0, pkey };

In practice, scan more slowly and use extra register on asynchronous input pressed. Also, have more than one input wire (use a close to square array).

Could use a separate microcontroller to scan keyboard.

This keyboard scanner generates an interrupt on each key press.

Standard PC keyboard generates an output byte on press and release and implements a short FIFO.

27: (C) 2008-11, DJ Greaves, University of Cambridge, Computer Laboratory.