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Rev 15 → Rev 16

/trunk/StepperMotorDrive.vhd
10,7 → 10,19
-- Please see the file "StepperMotorWiring.bmp" for info on connecting 4 & 6
-- wire motors to your device. This source should drive either type, though connection
-- to 4-wire motors requires significantly more FET's to buffer outputs. The
-- circuitry for 6-wire motors is more straightforward.
-- circuitry for 6-wire motors is more straightforward. The colors specified are
-- standard to many brands of stepper motors. If you get 1-2-3-4 on the FET's connected
-- to 4-3-2-1 on your logic device (backwards), the motor will simply rotate backwards.
-- if out of order, the motor won't rotate at all. Motors come in many dirrerent ratings
-- of degrees rotation per step; some offer exceptional resolution very inexpensively.
--
-- It is important to note that most logic operates at multiple megahertz. Given
-- a steper motor at 100 steps per revolution, and a clock of 10MHz, running the
-- motor at the full clock rate would equal 100,000 rps or 6 million revolutions per minute
-- obviously, motors don't do this. Most steppers are designed for fine resolution at low
-- speeds. Thus we employ a really big clock divider to get things operating at speeds
-- of which the motor is capable. Check your motor ratings for a usefull value.
-- in lieu of ratings, 100 rpm is usually achieveable, so plan accordingly.
--
-- Another practical consideration is the threshold voltage of the FET's used to
-- buffer the logic outputs & provide current drive to the motor. Most power
31,23 → 43,29
-- One of the most advantageous abilities of stepper motors is the ability to
-- provide static holding force in any position. Of course this consumes power
-- and heats the motor up significantly (though steppers are rated to handle this)
-- use of the "static holding" input port will specify this behavior.
-- use of the "static holding" input port will specify this behavior. Be aware,
-- however, that the motor will dissipate power if left energized for long periods
-- without (or without for that matter) rotating. This will make them hot! They are
-- usually designed for it, but it is a consideration, especially if in a small,
-- sealed, enclosure, excess heat may make your logic cease functioning correctly at
-- some point.
 
entity StepperMotorPorts is
Port (
StepDrive : out std_logic_vector(3 downto 0);
clock : in std_logic;
Direction : in std_logic;
StepEnable : in std_logic;
ProvideStaticHolding : in std_logic
StepDrive : out std_logic_vector(3 downto 0); -- the 4 output to drive the MOSFETS driving the coils in the motor.
clock : in std_logic; -- clock input to logic device
Direction : in std_logic; -- spin clockwise or counter-clockwise? (actual direction depends on correct hookup/pin assignements)
StepEnable : in std_logic; -- move a single step on next clock divider rollover. leave high for a single clock to get a single step. If high across rollover, may get two steps
ProvideStaticHolding : in std_logic -- leave motor coils energized when not rotating, so that counter-torque is applied if attempt to move shaft
);
end StepperMotorPorts;
 
architecture StepDrive of StepperMotorPorts is
 
signal state : std_logic_vector(1 downto 0);
signal StepCounter : std_logic_vector(31 downto 0);
constant StepLockOut : std_logic_vector(31 downto 0) := "00000000000000110000110101000000";
signal state : std_logic_vector(1 downto 0); -- simple state machine, 4 states
signal StepCounter : std_logic_vector(31 downto 0); -- most motors won't spin extrordinarially fast, so this slows the clock input way down
constant StepLockOut : std_logic_vector(31 downto 0) := "00000000000000110000110101000000"; --rollover for the counter, to get a non-binary delay time divider
signal InternalStepEnable : std_logic; -- used to capture a step enable even when we are in the wait loop for the clock divider.
 
begin
 
54,15 → 72,21
process(clock)
begin
 
if ( (clock'Event) and (clock = '1') ) then
if ( (clock'Event) and (clock = '1') ) then --on clock
 
StepCounter <= StepCounter + "0000000000000000000000000000001";
StepCounter <= StepCounter + "0000000000000000000000000000001"; --move the delay counter
 
if (StepEnable = '1') then
 
InternalStepEnable <= '1'; -- capture any requests for a step, even while we are waiting...
 
end if;
 
if (StepCounter >= StepLockOut) then
 
StepCounter <= "00000000000000000000000000000000";
StepCounter <= "00000000000000000000000000000000"; -- if we just roll-ed over, then it's time to do something
 
if (ProvideStaticHolding = '1') then
if (ProvideStaticHolding = '1') then --should we leave coils in energized state by defaul or not?
 
StepDrive <= "0000";
 
72,16 → 96,21
 
end if;
if (StepEnable = '1') then
if (Direction = '1') then state <= state + "01"; end if;
if (Direction = '0') then state <= state - "01"; end if;
if (InternalStepEnable = '1') then -- are we supposed to step on this clock?
 
InternalStepEnable <= StepEnable; -- InternalStepEnable togles at the speed of the clock divider rollover, trailing the
-- external StepEnable by less than or equal to one rollover.
-- Putting this inside the "if internal=1" makes us wait until after move to turn off,
-- so we move at least once for each pulse of external step enable line.
if (Direction = '1') then state <= state + "01"; end if; -- to change the direction of a stepper motor, you energize
if (Direction = '0') then state <= state - "01"; end if; -- the coils in the opposite pattern, so just run states backwards
-- this also allows a change of direction at any arbitrary point
case state is
 
when "00" =>
 
StepDrive <= "1010";
StepDrive <= "1010"; -- these states follow proper pattern of coil energizing for turning steppers
when "01" =>

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