How to change stepper motor direction using modbus

Forum|Forum|5 years ago
January 21, 2021
4 replies
901 views

Hi, i am controlling my stepper motor by giving commands through modbus in stm32f103. I am able to drive motor in one direction . But i am not able to drive my motor in another direction by sending command through modbus.

can anyone please help me with it.

i have another confusion whether i need to give negative values from my modbus to drive motor in another direction or not please anyone help me with it.

Thank you

STM32F1 series

This topic has been closed for replies.

Jack Peacock_2

Associate II

You have two options. The first is to encode direction in the 16-bit register used to specify the speed or number of steps. A positive register setting (0x0000-off, 1-0x7fff move positive direction) specifies clockwise stepping. A negative (0xffff-0x8000, 1 to 0x7fff in negative direction) specifies counterclockwise.

If you need the full 16-bit value for step count then use a one-bit register to select clockwise/counterclockwise direction. The disadvantage here is it now takes two commands to start the motor.

Jack Peacock

Lchal.1Author

Associate III

if(motion_type_absolute > 0 && motion_type_absolute < 65535 ) // positive direction

{

set direction pin as set;

}

else if(motion_type_absolute >32767 && motion_type_absolute < 65536) //negative direction

{

set direction pin as reset;

}

is this correct logic can i add to my code to drive stepper motor in both direction.

Thank you

Ozone

Principal

To add to Jack's correct answer - the modbus protocol does not "know" of positive/negative values.

It only specifies single bits and register (16-bit) values.

The signedness is in the interpretation of the sender/receiver (master and slave in modbus terms).

Lchal.1Author

Associate III

Thank you

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