mks-servo42-rs

A generic, no_std Rust driver for MKS SERVO42 closed-loop stepper motors.

This library provides a type-safe interface for generating the serial protocol commands used by the MKS SERVO42C firmware (V1.0+). It is transport-agnostic, meaning it generates byte buffers that you can send over any serial interface (UART, USB-Serial, etc.).

Features

• no_std compatible - Works in embedded environments
• Transport-agnostic - Generates raw command bytes, you handle the serial communication
• UART mode focused - Designed for CR_UART control mode (closed-loop UART interface)
• Type-safe - Rust enums for directions, modes, and status values
• Response parsing - Helpers for parsing encoder values, shaft status, and other responses

Supported Commands

Read Commands

Command	Code	Description
read_encoder_value	0x30	Read encoder position (carry + value)
read_pulse_count	0x33	Read received pulse count
read_motor_shaft_angle	0x36	Read motor shaft angle
read_motor_shaft_angle_error	0x39	Read shaft angle error
read_en_pin_status	0x3A	Read EN pin status
read_release_status	0x3D	Read release status
read_shaft_status	0x3E	Read shaft blocked/unblocked status

Configuration Commands

Command	Code	Description
calibrate_encoder	0x80	Calibrate encoder (motor must be unloaded)
set_current_limit	0x83	Set current limit (0-15 → 0-3000mA)
set_subdivision	0x84	Set microstepping (0-255), 0 = 256 subdivision
set_enable_logic	0x85	Set EN pin logic (Low/High/AlwaysOn)
set_direction	0x86	Set default rotation direction
set_auto_screen_off	0x87	Enable/disable auto screen off
set_stall_protection	0x88	Enable/disable stall protection
set_interpolation	0x89	Enable/disable step interpolation

Zero Mode Commands

Command	Code	Description
set_zero_mode	0x90	Set zero mode (Disable/DirMode/NearMode)
set_current_as_zero	0x91	Set current position as zero
set_zero_speed	0x92	Set return-to-zero speed (0-4)
set_zero_direction	0x93	Set return-to-zero direction
go_to_zero	0x94	Trigger return to zero

PID/Motion Commands

Command	Code	Description
set_position_kp	0xA1	Set position Kp (default 0x650)
set_position_ki	0xA2	Set position Ki (default 1)
set_position_kd	0xA3	Set position Kd (default 0x650)
set_acceleration	0xA4	Set acceleration (default 0x11E)
set_max_torque	0xA5	Set max torque (0-0x4B0)

Motor Control Commands

Command	Code	Description
enable_motor	0xF3	Enable/disable motor in UART mode
run_with_constant_speed	0xF6	Run at constant speed with direction
stop	0xF7	Stop motor immediately
run_motor	0xFD	Move relative pulses at speed
save_clear_status	0xFF	Save (0xC8) or clear (0xCA) status

Intentionally Unsupported Commands

These commands are intentionally not implemented as this crate is designed for UART mode only:

Command	Code	Reason
Set motor type	0x81	Hardware config, set via screen
Set work mode	0x82	This crate assumes CR_UART mode
Set baud rate	0x8A	Changing baud rate would break communication
Set UART address	0x8B	Address change requires reconnection
Restore defaults	0x3F	Would reset to non-UART mode

Helper Functions

The helpers module provides utility functions for parsing raw serial responses and performing motion calculations:

Function	Description
parse_encoder_response	Parse absolute encoder position (0x30)
parse_pulse_count_response	Parse received pulse count (0x33)
parse_motor_shaft_angle_response	Parse motor shaft angle (0x36)
parse_motor_shaft_angle_error	Parse motor shaft angle error (0x39)
parse_en_pin_status_response	Parse EN pin status (0x3A)
parse_shaft_status_response	Parse shaft blocked/unblocked status (0x3E)
parse_success_response	Parse standard 3-byte success/failure responses
strip_leading_garbage	Strip leading garbage bytes from serial buffers before valid packets
angle_to_steps	Convert angle (degrees) to pulse count for a given microstepping level
encoder_val_to_degrees	Convert a 16-bit encoder value to degrees (0–360)
speed_setting_to_rpm	Convert a speed setting byte + microsteps to RPM using the MKS formula
estimate_move_duration	Estimate move duration from speed, pulse count, and microsteps (no acceleration)

Usage Example

use mks_servo42_rs::{Driver, RotationDirection};

let mut driver = Driver::default();

// Enable motor
let cmd = driver.enable_motor(true);
// Send `cmd` bytes over your serial interface...

// Run at constant speed
let cmd = driver.run_with_constant_speed(RotationDirection::Clockwise, 10)?;

// Move 1000 pulses
let cmd = driver.run_motor(RotationDirection::Clockwise, 20, 1000)?;

// Stop
let cmd = driver.stop();

License

MIT or Apache-2.0