140 lines
6.6 KiB
VHDL
140 lines
6.6 KiB
VHDL
library IEEE;
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use IEEE.STD_LOGIC_1164.ALL;
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use IEEE.STD_LOGIC_ARITH.ALL;
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use IEEE.STD_LOGIC_UNSIGNED.ALL;
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-- c2003 Franks Development, LLC
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-- http://www.franks-development.com
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-- !This source is distributed under the terms & conditions specified at opencores.org
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--
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-- Please see the file "StepperMotorWiring.bmp" for info on connecting 4 & 6
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-- wire motors to your device. This source should drive either type, though connection
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-- to 4-wire motors requires significantly more FET's to buffer outputs. The
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-- circuitry for 6-wire motors is more straightforward. The colors specified are
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-- standard to many brands of stepper motors. If you get 1-2-3-4 on the FET's connected
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-- to 4-3-2-1 on your logic device (backwards), the motor will simply rotate backwards.
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-- if out of order, the motor won't rotate at all. Motors come in many dirrerent ratings
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-- of degrees rotation per step; some offer exceptional resolution very inexpensively.
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--
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-- It is important to note that most logic operates at multiple megahertz. Given
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-- a steper motor at 100 steps per revolution, and a clock of 10MHz, running the
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-- motor at the full clock rate would equal 100,000 rps or 6 million revolutions per minute
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-- obviously, motors don't do this. Most steppers are designed for fine resolution at low
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-- speeds. Thus we employ a really big clock divider to get things operating at speeds
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-- of which the motor is capable. Check your motor ratings for a usefull value.
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-- in lieu of ratings, 100 rpm is usually achieveable, so plan accordingly.
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--
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-- Another practical consideration is the threshold voltage of the FET's used to
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-- buffer the logic outputs & provide current drive to the motor. Most power
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-- FET's have a threshold voltage in the 5-12V range (or even higher),
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-- while logic devices now run in the 3.3V and lower range. Thus, you must be
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-- careful to choose a FET with a low threshold voltage, or a level-converter must
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-- be utilized between the logic output and the gate of the drive FET's.
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-- Practical tip: FET's with very high currect handling capabilities, in general
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-- (so be sure to read the datasheet before you buy), tend to handle larger currents
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-- for any given gate voltage. This means that in many cases, even if Vgs is rated at 5 volts
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-- if your stepper uses relatively low current, the FET's may still drive it at 3.3V or lower.
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-- In the worst case, you are likely going to need a high voltage power supply to drive the
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-- motors anyway, so you can "double-up" low power FET's to drive the gates of the power FET's
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-- with a higher voltage. In effect, the low-power FET's are wired as inverters with a low
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-- swithcing voltage. Contact Franks Development for a napkin-sketch if you aren't familiar
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-- with how to do that. Good luck.
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--
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-- One of the most advantageous abilities of stepper motors is the ability to
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-- provide static holding force in any position. Of course this consumes power
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-- and heats the motor up significantly (though steppers are rated to handle this)
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-- use of the "static holding" input port will specify this behavior. Be aware,
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-- however, that the motor will dissipate power if left energized for long periods
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-- without (or without for that matter) rotating. This will make them hot! They are
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-- usually designed for it, but it is a consideration, especially if in a small,
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-- sealed, enclosure, excess heat may make your logic cease functioning correctly at
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-- some point.
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entity StepperMotorPorts is
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Port (
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StepDrive : out std_logic_vector(3 downto 0); -- the 4 output to drive the MOSFETS driving the coils in the motor.
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clock : in std_logic; -- clock input to logic device
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Direction : in std_logic; -- spin clockwise or counter-clockwise? (actual direction depends on correct hookup/pin assignements)
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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
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ProvideStaticHolding : in std_logic -- leave motor coils energized when not rotating, so that counter-torque is applied if attempt to move shaft
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);
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end StepperMotorPorts;
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architecture StepDrive of StepperMotorPorts is
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signal state : std_logic_vector(1 downto 0); -- simple state machine, 4 states
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signal StepCounter : std_logic_vector(31 downto 0); -- most motors won't spin extrordinarially fast, so this slows the clock input way down
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constant StepLockOut : std_logic_vector(31 downto 0) := "00000000000000110000110101000000"; --rollover for the counter, to get a non-binary delay time divider
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signal InternalStepEnable : std_logic; -- used to capture a step enable even when we are in the wait loop for the clock divider.
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begin
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process(clock)
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begin
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if ( (clock'Event) and (clock = '1') ) then --on clock
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StepCounter <= StepCounter + "0000000000000000000000000000001"; --move the delay counter
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if (StepEnable = '1') then
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InternalStepEnable <= '1'; -- capture any requests for a step, even while we are waiting...
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end if;
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if (StepCounter >= StepLockOut) then
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StepCounter <= "00000000000000000000000000000000"; -- if we just roll-ed over, then it's time to do something
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if (ProvideStaticHolding = '1') then --should we leave coils in energized state by defaul or not?
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StepDrive <= "0000";
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else
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StepDrive <= "1111";
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end if;
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if (InternalStepEnable = '1') then -- are we supposed to step on this clock?
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InternalStepEnable <= StepEnable; -- InternalStepEnable togles at the speed of the clock divider rollover, trailing the
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-- external StepEnable by less than or equal to one rollover.
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-- Putting this inside the "if internal=1" makes us wait until after move to turn off,
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-- so we move at least once for each pulse of external step enable line.
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if (Direction = '1') then state <= state + "01"; end if; -- to change the direction of a stepper motor, you energize
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if (Direction = '0') then state <= state - "01"; end if; -- the coils in the opposite pattern, so just run states backwards
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-- this also allows a change of direction at any arbitrary point
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case state is
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when "00" =>
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StepDrive <= "1010"; -- these states follow proper pattern of coil energizing for turning steppers
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when "01" =>
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StepDrive <= "1001";
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when "10" =>
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StepDrive <= "0101";
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when "11" =>
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StepDrive <= "0110";
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when others =>
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end case; --state
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end if;
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end if;
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end if;
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end process;
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end StepDrive;
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