: Feetech STS Series Register Map and Instruction Set More...

Macros
Protocol Special IDs

#define	STS_ID_BROADCAST_SYNC 0xFEU

#define	STS_ID_BROADCAST_ASYNC 0xFFU

Protocol Instructions

#define	STS_INST_PING 0x01

#define	STS_INST_READ 0x02

#define	STS_INST_WRITE 0x03

#define	STS_INST_REGWRITE 0x04

#define	STS_INST_ACTION 0x05

#define	STS_INST_RESET 0x06

#define	STS_INST_SYNCREAD 0x82

#define	STS_INST_SYNCWRITE 0x83

EPROM Registers
Note Requires STS_REG_LOCK to be 0 to modify.
#define	STS_REG_ID 0x05

#define	STS_REG_BAUDRATE 0x06

#define	STS_REG_RETURN_DELAY 0x07

#define	STS_REG_RESPONSE_LEVEL 0x08

#define	STS_REG_MIN_ANGLE_LIMIT 0x09

#define	STS_REG_MAX_ANGLE_LIMIT 0x0B

#define	STS_REG_MAX_TEMP_LIMIT 0x0D

#define	STS_REG_MAX_VOLT_LIMIT 0x0E

#define	STS_REG_MIN_VOLT_LIMIT 0x0F

#define	STS_REG_MAX_TORQUE_LIMIT 0x10

#define	STS_REG_P_GAIN 0x15

#define	STS_REG_D_GAIN 0x16

#define	STS_REG_I_GAIN 0x17

#define	STS_REG_OFF_OFFSET 0x1F

#define	STS_REG_OPERATION_MODE 0x21

RAM Registers

#define	STS_REG_TORQUE_ENABLE 0x28

#define	STS_REG_ACCELERATION 0x29

#define	STS_REG_GOAL_POSITION 0x2A

#define	STS_REG_GOAL_TIME 0x2C

#define	STS_REG_GOAL_SPEED 0x2E

#define	STS_REG_LOCK 0x33

Feedback Registers

#define	STS_REG_PRESENT_POSITION 0x38

#define	STS_REG_PRESENT_SPEED 0x3A

#define	STS_REG_PRESENT_LOAD 0x3C

#define	STS_REG_PRESENT_VOLTAGE 0x3E

#define	STS_REG_PRESENT_TEMP 0x3F

#define	STS_REG_ASYNC_WRITE_FLAG 0x40

#define	STS_REG_STATUS_ERROR 0x41

#define	STS_REG_MOVING_FLAG 0x42

#define	STS_REG_TORQUE_LIMIT 0x30

Hardware Error Bitmasks (Address 0x41)

#define	STS_STATUS_OK 0x00U

#define	STS_BIT_ERR_VOLTAGE (1 << 0)

#define	STS_BIT_ERR_TEMP (1 << 1)

#define	STS_BIT_ERR_OVERHEAT (1 << 2)

#define	STS_BIT_ERR_LOAD (1 << 3)

Common State Values

#define	STS_TORQUE_DISABLE 0x00U

#define	STS_TORQUE_ENABLE 0x01U

Speed Register Bitmasks (Addresses 0x2E and 0x3A)
Masks for parsing target and present speed registers.
#define	STS_SPEED_DIRECTION_BIT 0x8000U

#define	STS_SPEED_MAGNITUDE_MASK 0x7FFFU

Load Register Bitmasks (Address 0x2A)
Masks for parsing present load telemetry. @(
#define	STS_LOAD_DIRECTION_BIT 0x0400U

#define	STS_LOAD_MAGNITUDE_MASK 0x03FF

Enumerations
enum	sts_operating_mode_t { STS_MODE_POSITION = 0U , STS_MODE_SPEED = 1U , STS_MODE_PWM = 2U , STS_MODE_STEP = 3U }
	Defines the active internal control algorithm (Operating Mode). Changing the operating mode fundamentally alters how the servo responds to target commands. It rewires the internal control loop . More...

Detailed Description

: Feetech STS Series Register Map and Instruction Set

Author: : Grisham Balloo

This header defines the internal memory map and command set for the Feetech STS-series smart servos.

The register map is divided into two primary sections:

EPROM (0x05 - 0x21): Persistent settings that survive power cycles. Requires unlocking via STS_REG_LOCK to modify.
RAM (0x28 - 0x42): Volatile control and feedback registers updated in real-time. Changes are lost upon power-off.

Data Types:
1-Byte registers: Standard uint8_t access.
2-Byte registers: Little-endian (Low byte first).
Attention
Copyright (c) 2026 Grisham Balloo. All rights reserved.

Macro Definition Documentation

◆ STS_BIT_ERR_LOAD

#define STS_BIT_ERR_LOAD (1 << 3)

Overload/Stall detected

◆ STS_BIT_ERR_OVERHEAT

#define STS_BIT_ERR_OVERHEAT (1 << 2)

Over-temperature detected

◆ STS_BIT_ERR_TEMP

#define STS_BIT_ERR_TEMP (1 << 1)

Internal temperature sensor fault

◆ STS_BIT_ERR_VOLTAGE

#define STS_BIT_ERR_VOLTAGE (1 << 0)

Voltage outside safety limits

◆ STS_ID_BROADCAST_ASYNC

#define STS_ID_BROADCAST_ASYNC 0xFFU

255: Broadcast to all servos (Wait for ACTION instruction)

◆ STS_ID_BROADCAST_SYNC

#define STS_ID_BROADCAST_SYNC 0xFEU

254: Broadcast to all servos (Execute immediately)

◆ STS_INST_ACTION

#define STS_INST_ACTION 0x05

Trigger buffered RegWrite commands

◆ STS_INST_PING

#define STS_INST_PING 0x01

Check servo online status

◆ STS_INST_READ

#define STS_INST_READ 0x02

Read data from register

◆ STS_INST_REGWRITE

#define STS_INST_REGWRITE 0x04

Buffer write data for Action command

◆ STS_INST_RESET

#define STS_INST_RESET 0x06

Factory reset EPROM parameters

◆ STS_INST_SYNCREAD

#define STS_INST_SYNCREAD 0x82

Read from multiple servos simultaneously

◆ STS_INST_SYNCWRITE

#define STS_INST_SYNCWRITE 0x83

Write to multiple servos simultaneously

◆ STS_INST_WRITE

#define STS_INST_WRITE 0x03

Write data to register

◆ STS_LOAD_DIRECTION_BIT

#define STS_LOAD_DIRECTION_BIT 0x0400U

Bit 10: 0 = CW (Negative), 1 = CCW (Positive)

◆ STS_LOAD_MAGNITUDE_MASK

#define STS_LOAD_MAGNITUDE_MASK 0x03FF

Bits 0-9: Raw load magnitude value

◆ STS_REG_ACCELERATION

#define STS_REG_ACCELERATION 0x29

Acceleration/deceleration ramp

◆ STS_REG_ASYNC_WRITE_FLAG

#define STS_REG_ASYNC_WRITE_FLAG 0x40

Status of buffered RegWrite

◆ STS_REG_BAUDRATE

#define STS_REG_BAUDRATE 0x06

Communication speed selector

◆ STS_REG_D_GAIN

#define STS_REG_D_GAIN 0x16

Differential gain for PID

◆ STS_REG_GOAL_POSITION

#define STS_REG_GOAL_POSITION 0x2A

Target position (2 bytes, 0-4095)

◆ STS_REG_GOAL_SPEED

#define STS_REG_GOAL_SPEED 0x2E

Target movement speed (2 bytes)

◆ STS_REG_GOAL_TIME

#define STS_REG_GOAL_TIME 0x2C

Target movement duration (2 bytes)

◆ STS_REG_I_GAIN

#define STS_REG_I_GAIN 0x17

Integral gain for PID

◆ STS_REG_ID

#define STS_REG_ID 0x05

Servo ID (0-253, 254 for broadcast)

◆ STS_REG_LOCK

#define STS_REG_LOCK 0x33

0: Unlock EPROM, 1: Lock EPROM

◆ STS_REG_MAX_ANGLE_LIMIT

#define STS_REG_MAX_ANGLE_LIMIT 0x0B

CCW angle limit (2 bytes)

◆ STS_REG_MAX_TEMP_LIMIT

#define STS_REG_MAX_TEMP_LIMIT 0x0D

Max temperature threshold (°C)

◆ STS_REG_MAX_TORQUE_LIMIT

#define STS_REG_MAX_TORQUE_LIMIT 0x10

Max output torque (2 bytes)

◆ STS_REG_MAX_VOLT_LIMIT

#define STS_REG_MAX_VOLT_LIMIT 0x0E

Max voltage threshold (0.1V units)

◆ STS_REG_MIN_ANGLE_LIMIT

#define STS_REG_MIN_ANGLE_LIMIT 0x09

CW angle limit (2 bytes)

◆ STS_REG_MIN_VOLT_LIMIT

#define STS_REG_MIN_VOLT_LIMIT 0x0F

Min voltage threshold (0.1V units)

◆ STS_REG_MOVING_FLAG

#define STS_REG_MOVING_FLAG 0x42

1: Moving, 0: Target reached

◆ STS_REG_OFF_OFFSET

#define STS_REG_OFF_OFFSET 0x1F

Center position correction (2 bytes)

◆ STS_REG_OPERATION_MODE

#define STS_REG_OPERATION_MODE 0x21

0: Position, 1: Speed, 2: PWM

◆ STS_REG_P_GAIN

#define STS_REG_P_GAIN 0x15

Proportional gain for PID

◆ STS_REG_PRESENT_LOAD

#define STS_REG_PRESENT_LOAD 0x3C

Current motor load (2 bytes)

◆ STS_REG_PRESENT_POSITION

#define STS_REG_PRESENT_POSITION 0x38

Current encoder position (2 bytes)

◆ STS_REG_PRESENT_SPEED

#define STS_REG_PRESENT_SPEED 0x3A

Current rotational speed (2 bytes)

◆ STS_REG_PRESENT_TEMP

#define STS_REG_PRESENT_TEMP 0x3F

Internal temperature (°C)

◆ STS_REG_PRESENT_VOLTAGE

#define STS_REG_PRESENT_VOLTAGE 0x3E

Current input voltage (0.1V units)

◆ STS_REG_RESPONSE_LEVEL

#define STS_REG_RESPONSE_LEVEL 0x08

0: None, 1: Read commands only, 2: All

◆ STS_REG_RETURN_DELAY

#define STS_REG_RETURN_DELAY 0x07

Delay time before status return (0.5us units)

◆ STS_REG_STATUS_ERROR

#define STS_REG_STATUS_ERROR 0x41

Hardware error

◆ STS_REG_TORQUE_ENABLE

#define STS_REG_TORQUE_ENABLE 0x28

1: Torque On, 0: Free move

◆ STS_REG_TORQUE_LIMIT

#define STS_REG_TORQUE_LIMIT 0x30

Dynamic output torque limit (2 bytes, 0-1000)

◆ STS_SPEED_DIRECTION_BIT

#define STS_SPEED_DIRECTION_BIT 0x8000U

Bit 15: 0 = CCW (Positive), 1 = CW (Negative)

◆ STS_SPEED_MAGNITUDE_MASK

#define STS_SPEED_MAGNITUDE_MASK 0x7FFFU

Bits 0-14: Raw speed magnitude value

◆ STS_STATUS_OK

#define STS_STATUS_OK 0x00U

No hardware errors

◆ STS_TORQUE_DISABLE

#define STS_TORQUE_DISABLE 0x00U

Disable motor torque (free spin)

◆ STS_TORQUE_ENABLE

#define STS_TORQUE_ENABLE 0x01U

Enable motor torque (hold position)

Enumeration Type Documentation

◆ sts_operating_mode_t

enum sts_operating_mode_t

Defines the active internal control algorithm (Operating Mode). Changing the operating mode fundamentally alters how the servo responds to target commands. It rewires the internal control loop .

Enumerator
STS_MODE_POSITION	Absolute position control via PID. Target speed acts as a travel limit.
STS_MODE_SPEED	Continuous rotation velocity control. Absolute position commands are ignored.
STS_MODE_PWM	Open-loop voltage control. PID is disabled; servo acts as a standard DC motor.
STS_MODE_STEP	Relative position control. Moves a specified number of steps from the current location.

Macros

Enumerations