FEETECH STS Servo – Memory Table Analysis

STS Servo – Memory Table Analysis

Magnetic Encoder STS Servo

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1. Servo Communication Protocol

The servo uses the FT-SCS custom protocol. The factory default serial configuration is as follows: baud rate 1 Mbps, using TTL single-wire bus communication, 8 data bits, no parity, and 1 stop bit.

The baud rate is configurable from 38,400 to 1 Mbps. The default communication address (station ID) is 1.

2. Servo Memory Table Definition

If the function address uses two bytes of data, the low byte is stored at the lower address, and the high byte is stored at the higher address.

2.1 Version Information

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
0	0x00	Firmware Major Version Number	1	–	RO
1	0x01	Firmware Minor Version Number	1	–	RO
2	0x02	END	1	0	RO			0 indicates little-endian storage structure
3	0x03	Servo Major Version Number	1	–	RO
4	0x04	Servo Minor Version Number	1	–	RO

2.2 EPROM Configuration

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
5	0x05	Servo ID	1	1	RW	0 ~ 253	No.	Unique master ID on the bus
6	0x06	Baud Rate	1	0	RW	0 ~ 7		0–7 correspond to: 1000000 (0), 500000 (1), 250000 (2), 128000 (3), 115200 (4), 76800 (5), 57600 (6), 38400 (7)
7	0x07	Reserved Address	1	–	RW	–	–
8	0x08	Response Status Level	1	1	RW	0 ~ 1		0: No response except READ and PING; 1: Respond to all instructions
9	0x09	Minimum Angle Limit	2	0	RW	0 ~ 4094	0.087 degrees	0 when multi-turn absolute position control is used
11	0x0B	Maximum Angle Limit	2	4095	RW	1 ~ 4095	0.087 degrees	0 when multi-turn absolute position control is used
13	0x0D	Maximum Temperature Limit	1	70	RW	0 ~ 100	°C
14	0x0E	Maximum Input Voltage	1	–	RW	0 ~ 254	0.1 V
15	0x0F	Minimum Input Voltage	1	40	RW	0 ~ 254	0.1 V
16	0x10	Maximum Torque	2	1000	RW	0 ~ 1000	0.1 %	Assigned to address 48 (Torque Limit) at power-on
18	0x12	Phase	1	–	RW	0 ~ 254		Special function byte, do not modify unless required
19	0x13	Unload Condition	1	–	RW	0 ~ 254		Bit=1 enables corresponding protection; Bit=0 disables
20	0x14	LED Alarm Condition	1	–	RW	0 ~ 254		Bit=1 enables alarm flashing; Bit=0 disables
21	0x15	Position Loop Proportional Gain (Kp)	1	–	RW	0 ~ 254		Proportional gain (scaled by 1/4)
22	0x16	Position Loop Derivative Gain (Kd)	1	–	RW	0 ~ 254		Derivative gain (scaled by 1/8)
23	0x17	Position Loop Integral Gain (Ki)	1	0	RW	0 ~ 254		Integral gain
24	0x18	Minimum Starting Torque	1	–	RW	0 ~ 254	0.1 %	Minimum startup torque
25	0x19	Integral Limit Value	1	0	RW	0 ~ 254		Max integral = value × 4; 0 disables; valid in mode 0 and 4
26	0x1A	Positive Dead Zone	1	1	RW	0 ~ 16	0.087 degrees	Minimum unit equals minimum resolvable angle
27	0x1B	Negative Dead Zone	1	1	RW	0 ~ 16	0.087 degrees	Minimum unit equals minimum resolvable angle
28	0x1C	Protection Current	2	511	RW	0 ~ 2047	6.5 mA	Max current = 500 × 6.5 mA = 3250 mA
30	0x1E	Angular Resolution	1	1	RW	1 ~ 128		Amplification factor of sensor resolution
31	0x1F	Position Offset	2	0	RW	0 ~ 8191	0.087 degrees	Encoded offset: maps to -4095 ~ 4095 (see encoding rules)
33	0x21	Operating Mode	1	0	RW	0 ~ 3		0: Position mode; 1: Constant speed mode; 2: PWM open-loop mode; 3: Step mode
34	0x22	Holding Torque	1	20	RW	0 ~ 254	1 %	Output torque after overload protection (e.g., 20 = 20%)
35	0x23	Protection Time	1	200	RW	0 ~ 254	10 ms	Duration exceeding overload torque (e.g., 200 = 2 s, max 2.5 s)
36	0x24	Overload Torque Threshold	1	80	RW	0 ~ 254	1 %	Threshold to trigger overload protection timing
37	0x25	Velocity Loop Proportional Gain (Kp)	1	–	RW	0 ~ 254		Used in constant speed mode (Mode 1)
38	0x26	Overcurrent Protection Time	1	200	RW	0 ~ 254	10 ms	Max = 254 × 10 ms = 2540 ms
39	0x27	Velocity Loop Integral Gain (Ki)	1	–	RW	0 ~ 254		Used in constant speed mode (Mode 1)

2.3 SRAM Control

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
40	0x28	Torque Switch	1	0	RW	0 ~ 2		0: Disable torque; 1: Enable torque; 2: Damping mode (torque limit at address 48 controls damping strength); 128: Calibrate current position to 2048
41	0x29	Acceleration	1	0	RW	0 ~ 254	8.7 degrees/s²	Acceleration/deceleration of servo; 0 indicates maximum acceleration
42	0x2A	Target Position	2	0	RW	-32767 ~ 32767	0.087 degrees	Absolute position control; max corresponds to max valid angle; Bit15 is direction bit
44	0x2C	PWM Open-loop Speed	2	1000	RW	0 ~ 1000	0.1 %	Effective in PWM open-loop mode; Bit10 is direction bit
46	0x2E	Operating Speed	2	Max factory speed	RW	-32767 ~ 32767	0.732 RPM / 0.0146 RPM	Maximum motor speed; Bit15 is direction bit; 0 means max speed by default; can be set to stop via phase; unit selectable (0.732 or 0.0146 RPM), resolution remains 0.732 RPM
48	0x30	Torque Limit	2	Maximum Torque (16), default 1000	RW	0 ~ 1000	0.1 %	User-configurable stall torque output
50 ~ 54	0x32 ~ 0x36	Undefined	1	–	RW	–	–
55	0x37	Lock Flag	1	1	RW	0 ~ 1		0: Disable write lock (EPROM values saved after power-off); 1: Enable write lock (EPROM values not saved after power-off)

2.4 SRAM Feedback

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
56	0x38	Present Position	2	–	R	–	0.087 degrees	Feedback of current absolute position; Bit15 is direction; in Step mode (Mode 3), returns step difference between current and target position (Bit15 is direction)
58	0x3A	Present Speed	2	–	R	–	0.732 RPM / 0.0146 RPM	Feedback of current motor speed; unit depends on phase setting; Bit15 is direction
60	0x3C	Present Load	2	–	R	–	0.1 %	PWM duty cycle driving the motor; Bit10 is direction
62	0x3E	Present Voltage	1	–	R	–	0.1 V	Current operating voltage
63	0x3F	Present Temperature	1	–	R	–	°C	Internal temperature of the servo
64	0x40	Async Write Flag	1	0	R	–		Flag used during asynchronous write operations
65	0x41	Servo Status	1	0	R	–		Bit flags; Bit=1 indicates corresponding error
66	0x42	Moving Flag	1	0	R	–		1: moving; 0: stopped at target or no target update
67	0x43	Target Position	2	0	R	–	0.087 degrees	Current target position
69	0x45	Present Current	2	–	R	–	6.5 mA	Phase current feedback
71	0x47	Undefined	2	–	R	–	–

2.5 Factory Parameters

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
80	0x50	Motion Speed Threshold	1	–	R	–	–	Threshold for determining whether the servo is in motion
81	0x51	DTs (ms)	1	–	R	–	ms	Internal control cycle timing parameter
82	0x52	Velocity Scaling Factor	1	–	R	–	–	Scaling factor for velocity unit conversion
83	0x53	Minimum Speed Limit	1	–	R	–	0.732 RPM	Minimum allowable speed limit
84	0x54	Maximum Speed Limit	1	–	R	–	0.732 RPM	Maximum allowable speed limit
85	0x55	Acceleration Limit	1	–	R	–	–	Factory-defined maximum acceleration limit
86	0x56	Acceleration Multiplier	1	–	R	–	–	Effective when acceleration = 0; if both multiplier and acceleration are 0, the servo achieves maximum response speed

3. Special Byte Description

3.1 Servo Phase

Bit number / bit weight: description

BIT0 (1): driver direction phase; (0) forward, (1) reverse
BIT1 (2): driver bridge mode; (0) brushless, (1) brushed (effective after reboot)
BIT2 (4): speed unit; (0) 0.732 RPM, (1) 0.0146 RPM
BIT3 (8): speed mode; (0) speed = 0 means stop, (1) speed = 0 means maximum speed
BIT4 (16): angle feedback mode; (0) single-turn angle feedback, (1) full-range angle feedback
BIT5 (32): driver bridge configuration / voltage sampling; (0) independent H-bridge / 1K high-voltage sampling, (1) integrated H-bridge / 1.5K low-voltage sampling / no current feedback
BIT6 (64): PWM frequency; (0) 24 kHz, (1) 16 kHz
BIT7 (128): position feedback direction phase; (0) forward, (1) reverse

💡

Note:If multiple bits are set simultaneously, the servo phase value equals the sum of all bit values.

For example: If the original phase value is 0 and reverse operation is required, the phase value is 128 + 1 = 129.

3.2 Servo Status

Servo status: 0 indicates normal, 1 indicates abnormal

Bit number / bit weight: description

BIT0 (1): voltage status
BIT1 (2): magnetic encoder status
BIT2 (4): temperature status
BIT3 (8): current status
BIT4 (16): ----
BIT5 (32): load status
BIT6 (64): ----
BIT7 (128): ----

💡

Note:If multiple statuses occur simultaneously, the servo status value equals the sum of all bit values.

For example:voltage over/under-voltage and servo overheat, then the servo status value is 4 + 1 = 5.

3.3 Unload Condition

Unload condition: 0 indicates off, 1 indicates on

Bit number / bit weight: description

BIT0 (1): voltage protection
BIT1 (2): magnetic encoder protection
BIT2 (4): overheat protection
BIT3 (8): overcurrent protection
BIT4 (16): ----
BIT5 (32): load overload protection
BIT6 (64): ----
BIT7 (128): ----

💡

Note:If multiple bits are set, the unload condition value equals the sum of all bit values.

For example:voltage protection and overheat protection enabled at the same time, then the unload condition value is 4 + 1 = 5.

3.4 LED Alarm Condition

Alarm condition: 0 indicates off, 1 indicates on

Bit number / bit weight: description

BIT0 (1): voltage alarm
BIT1 (2): magnetic encoder alarm
BIT2 (4): overheat alarm
BIT3 (8): overcurrent alarm
BIT4 (16): ----
BIT5 (32): load overload alarm
BIT6 (64): ----
BIT7 (128): ----

💡

Note: If multiple bits are set simultaneously, the alarm condition value equals the sum of all bit values.

For example: voltage alarm and overheat alarm enabled at the same time, then the alarm condition value is 4 + 1 = 5.

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On this page

STS Servo – Memory Table Analysis
1. Servo Communication Protocol
2. Servo Memory Table Definition
2.1 Version Information
2.2 EPROM Configuration
2.3 SRAM Control
2.4 SRAM Feedback
2.5 Factory Parameters
3. Special Byte Description
3.1 Servo Phase
3.2 Servo Status
3.3 Unload Condition
3.4 LED Alarm Condition