VHDL programming issues...newbie

Question

I'm trying to write a state machine in VHDL that will scan a 4x4 keypad. I want keyP set to 0 at the start and after a Reset. I also want the Col to be set to "1111" at the start and after a Reset.

As I'm not fully versed in VHDL programming I'm sure it's just a stupid syntax error. The error I get is:

Error (10818): Can't infer register for "Col[0]" at Lab_7_Keypad.vhd(39) because it does not hold its value outside the clock edge

and the same for Col[1] Col[2] Col[3] and for keyP as well.

Here's my code for the start of it all. Can someone give me an idea where I've gone wrong?

ENTITY Lab_7_Keypad IS
PORT(
nReset : IN STD_LOGIC;
clk : IN STD_LOGIC;
row : IN STD_LOGIC_VECTOR (3 downto 0);
Col : OUT STD_LOGIC_VECTOR (3 downto 0);
data : OUT STD_LOGIC_VECTOR (3 downto 0);
keyP : OUT STD_LOGIC);
END Lab_7_Keypad;
ARCHITECTURE a OF Lab_7_Keypad IS 
TYPE STATE_TYPE IS ( Col1Set, Col2Set, Col3Set, Col4Set );
SIGNAL coltest : STATE_TYPE;
BEGIN
PROCESS (clk, nReset )
BEGIN
keyP <= '0';
Col <= "1111";
IF nReset = '0' THEN -- asynch Reset to zero
 coltest <= Col1Set;
 Col <="1111";
 keyP <= '0';
ELSIF clk'EVENT AND clk = '1' THEN -- triggers on PGT
 CASE coltest IS
 WHEN Col1Set => 
 Col <="1110";
 CASE row IS
 WHEN "1110"=>--row 1
 data <= "0001";
 keyP <= '1';
 WHEN "1101"=>--row 2
 data <= "0100";
 keyP <= '1';
 WHEN "1011"=>--row 3
 data <= "0111";
 keyP <= '1';
 WHEN "0111"=>--row 4
 data <= "1110";
 keyP <= '1';
 WHEN OTHERS => coltest <= Col2Set;
 END CASE;
 --Continues for another couple Case statements for the extra columns

Answer 1

Delete the two middle lines, below

BEGIN
--keyP <= '0';
--Col <= "1111";
IF nReset = '0' THEN -- asynch Reset to zero

These state that keyP and Col are always assigned (like connected to GND or Power), later you state they are connected to registers. You are asking for VHDL to connect a register to a signal connected to GND or Power.

• Chef Flambe: Thanks. I knew it was something simple like that. Now I need to figure out how to debounce the thing. Feel free to offer ideas, however I'll be doing some reading just the same.
• Jay M: To de-bounce you need to capture a change in the output, perhaps with another module. And then re-sample that output at some time later. Bouncing of switches happens just as the switch is pressed or just as it is released so sampling an outout during that change resules in an unpredictable measurement.