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Driving a Stepper from FPGA

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ishailesh

ishailesh

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Hey all

Mine board is Virtex2Pro. I want to drive a stepper motor from FPGA.
I am using L293D as the driver circuit.
So for that i designed a state machine which changes its output on each rising edge of the clock.
The Clock Speed is 100MHz (Internal Clock). But somehow i am not getting the desired pulses at the output.
Here is my code.





Code VHDL - [expand]
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library ieee;
use ieee.std_logic_1164.all;
 
entity motor_state is
 
    port(
    
        en      : in    std_logic;
        clk     : in    std_logic;
        dir     : in    std_logic;
        reset       : in    std_logic;
        data_out     : out std_logic_vector(3 downto 0)
    );
    
end entity;
 
architecture motor_state_sequential of motor_state is
 
    -- Build an enumerated type for the state machine
    type state_type is (s0, s1, s2, s3);
    
    -- Register to hold the current state
    signal state   : state_type;
 
begin
    -- Logic to advance to the next state
    process (clk, reset)
    begin
    if (en = '1')then
        if reset = '1' then
        state <= s0;
           elsif (rising_edge(clk)) then
            case state is
                when s0=>
                    if dir = '1' then
                        state <= s1;
                    else
                        state <= s3;
                    end if;
                when s1=>
                    if dir = '1' then
                        state <= s2;
                    else
                        state <= s0;
                    end if;
                when s2=>
                    if dir = '1' then
                        state <= s3;
                    else
                        state <= s1;
                    end if;
                when s3 =>
                    if dir = '1' then
                        state <= s0;
                    else
                        state <= s2;
                    end if;
            end case;
        end if;
    end if;
    
    end process;
    
    -- Output depends on the current state
    process (state)
    begin
     
if (en = '1')then
            case state is
            when s0 =>
                data_out <= "0001";
            when s1 =>
                data_out <= "0100";
            when s2 =>
                data_out <= "0010";
            when s3 =>
                data_out <= "1000";
        end case;
 
end if;     
    
    end process;
    
end motor_state_sequential;







I was successfully able to program the fpga. But it didn't produce the desired result.
So please help.


Thanks and Regards
 
Last edited by a moderator:

You need to slow down your clock to the state machine to a few hundred Hz or even lower depending on what you want
 

As alex mentioned, you need to slow down your clock. Also, you should consult the data sheet for your motor so that you can determine the appropriate operating frequency (usually referred to as the "stepping" frequency) at which to drive your motor. Most stepper motors have a resonant frequency that will damage the stepper motor if it is driven at this frequency. While this is most likely not the case, it is valuable to know at what frequency to drive your motor.

-Willis
 

Thanks for your Suggestions.
I did slowed down my clock using a dcm module (from 100MHz to 6.25Mhz).
But still i am not sure how at what frequency my output will be.
Since there must be a definite time involved in compilation and execution of code.
So please help in the same.

P.S.
Previously i was using ATMega32 for driving my stepper.The clock frequency used here was 1MHz.
I also included a delay of 1ns between consecutive pulses and motor just worked fine.

I was wondering if i can use PowerPC..If yes then please tell how??
 

Don't confuse the core frequency of a microcontroller with the output step rate.

In your VHDL code you are changing the output state with every clock so you will get 6.25M steps /sec
 

ishailesh said:
Thanks for your Suggestions.
I did slowed down my clock using a dcm module (from 100MHz to 6.25Mhz).
But still i am not sure how at what frequency my output will be.
Since there must be a definite time involved in compilation and execution of code.
So please help in the same.

P.S.
Previously i was using ATMega32 for driving my stepper.The clock frequency used here was 1MHz.
I also included a delay of 1ns between consecutive pulses and motor just worked fine.

I was wondering if i can use PowerPC..If yes then please tell how??
Click to expand...

Once you decide at what frequency you would like to drive your motor, you can write a simple process to drive the motor at the correct frequency. For instance, if you have a 100 MHz clock, you could write a process that would keep a count and only change the output once the count reaches 10000; then you would clear the count and increment it at every clock cycle, once again updating the output when the count reaches 10000. This would give you an output frequency of roughly 10 kHz. Once again, you should look at the data sheet for the stepper motor to decide what operating frequency is optimal for your motor.

-Willis
 

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