keyboard.tdf

基于max plus2的ahdl语言。这个是键盘扫描程序的ahdl。文件格式是tdf。可以扫描键盘。

TITLE "Keyboard Encoder";

INCLUDE "74151";
INCLUDE "74154";
INCLUDE "4count";

FUNCTION debounce (clk, key_pressed)
	RETURNS (pulse);

SUBDESIGN keyboard
(
   clk                 :   INPUT;  % 50-KHz clock            %
   col[3..0]           :   INPUT;  % keyboard columns        %
   row[3..0], d[3..0]  :   OUTPUT; % keyboard rows, key code %
   strobe              :   OUTPUT; % key code is valid       %
)
VARIABLE
   key_pressed   :   NODE; % VCC when key d[3..0] is pressed %
   mux           :   74151;
   decoder       :   74154;
   counter       :   4count;
   opencol[3..0] :   TRI;
BEGIN
	% Drive keyboard rows with a decoder and      %
	% open-collector outputs.                     %

	row[] = opencol[].out;
	opencol[].in = GND;
	opencol[].oe = decoder.(o0n,o1n,o2n,o3n);
	decoder.(b,a) = counter.(qd,qc);

	% Sense keyboard columns with a multiplexer   %

	mux.d[3..0] = col[3..0];
	mux.(b,a) = counter.(qb,qa);
	key_pressed = !mux.y;

	% Scan keyboard until a key is pressed.       %
	% Drive key's code onto d[] outputs           %

	counter.clk = clk;
	counter.cin = !key_pressed;
	d[] = counter.(qd,qc,qb,qa);

	% Generate strobe when key has settled        %

	strobe = debounce(clk, key_pressed);
END;