Serial stepper motor interface API

*Subject: API for controlling a serial stepper motor
*Version: 1.0
*Status: final
*Author: Jeroen Vreeken
*Date: 14-6-2001

Introduction

This is the API for a stepper motor controller connected to a standard serial port.
The protocol is designed to allow the control of multiple (up to 256) independand motors.
The motors must have a safety to prevent turning to far.
The user must be able to read the status of the motor.

API

The interface works at a fixed baudrate of 9600bps. Each command will consist of three bytes. After each command the interface will return a status byte. Where needed counting will start at zero.

Build-up of a command:

• byte0 will contain the motor number. Usually zero.

• byte1 will contain the command. A list of valid commands is given later on in this document.

• byte2 will contain additional data for this command.

Build-up of the status byte:

• bit0 will signal if the motor turns left.

• bit1 will signal if the motor turns right.

• bit2 indicates that the motor is against the left safety stop.

• bit3 indicates that the motor is against the right safety stop.

• bit4 - bit7 these bits are not used and shall be zero.

These are the valid commands:

• 0 STATUS
  Nothing will happen, just the status byte will be returned. The data byte will be ignored.

• 1 LEFT_N
  The motor will make N steps to the left unless it hits the left safety first.
  The data byte will contain N.

• 2 RIGHT_N
  The motor will make N steps to the right unless it hits the right safety first.
  The data byte will contain N.

• 3 LEFT
  The motor will continuously turn left until it hits the left safety stop.
  The data byte is ignored.

• 4 RIGHT
  The motor will continuously turn right until it hits the right safety stop.
  The data byte is ignored.

• 5 SWEEP
  The motor will start making a sweeping movement.
  The data byte is ignored.

• 6 STOP
  The motor will stop moving.
  The data byte is ignored.

• 7 SPEED
  This command controls the speed of the motor, 0 is the slowest, 255 the fastest.

Note that motion does not use all of these commands, implementing a subset of these commands will also work.