FEETECH HLS Servo – Memory Table Analysis

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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, 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	3	RO
1	0x01	Firmware Minor Version Number	1	–	RO	40–59
2	0x02	END	1	0	RO			0 indicates little-endian storage structure
3	0x03	Servo Major Version Number	1	10	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 (Main ID)	1	1	RW	0 ~ 253	No.	Unique master ID on the bus (primary identifier)
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	Sub ID	1	0	RW	0 ~ 253	No.	Secondary ID (used only for write instructions)
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	0.1V
15	0x0F	Minimum Input Voltage	1	40	RW	0 ~ 254	0.1V
16	0x10	Maximum Torque	2	980	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 protection; Bit=0 disables protection
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		Assigned to address 50 at power-on
22	0x16	Position Loop Derivative Gain (Kd)	1	-	RW	0 ~ 254		Assigned to address 51 at power-on
23	0x17	Position Loop Integral Gain (Ki)	1	0	RW	0 ~ 254		Assigned to address 52 at power-on
24	0x18	Minimum Starting Torque	1	-	RW	0 ~ 254	0.1%	Minimum startup torque of the servo
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 = minimum resolvable angle
27	0x1B	Negative Dead Zone	1	1	RW	0 ~ 16	0.087 degrees	Minimum unit = minimum resolvable angle
28	0x1C	Protection Current	2	-	RW	0 ~ 2047	6.5mA	Assigned to address 44 (Target Current) at power-on
30	0x1E	Angular Resolution	1	1	RW	1 ~ 128		Amplification factor of sensor resolution
31	0x1F	Position Offset	2	0	RW	-4095 ~ 4095	0.087 degrees	Bit15 indicates direction
33	0x21	Operating Mode	1	0	RW	0 ~ 3		0: Position mode; 1: Constant speed mode; 2: Constant current mode; 3: PWM open-loop mode
34	0x22	Current Loop Proportional Gain (Kp)	1	-	RW
35	0x23	Current Loop Integral Gain (Ki)	1	-	RW
36	0x24	Undefined	1	-	RW	-	-	-
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	10ms
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
41	0x29	Acceleration	1	0	RW	0 ~ 254	8.7°/s²	0 indicates maximum acceleration
42	0x2A	Target Position	2	0	RW	-32767 ~ 32767	0.087 degrees	Bit15 is direction bit
44	0x2C	Target Current	2	Protection Current (28)	RW	-2047 ~ 2047	6.5mA	Bit15 is direction (mode 2); PWM mode uses -1000~1000 (Bit10 direction)
46	0x2E	Operating Speed	2	Max factory speed	RW	-32767 ~ 32767	0.732 RPM	0 = stop; Bit15 direction
48	0x30	Torque Limit	2	Maximum Torque (16)	RW	0 ~ 1000	0.1%	Stall torque control
50	0x32	Kp	1	From EPROM (21)	RW	0 ~ 254		Position loop proportional gain (1/8)
51	0x33	Kd	1	From EPROM (22)	RW	0 ~ 254		Position loop derivative gain (1/4)
52	0x34	Ki	1	From EPROM (23)	RW	0 ~ 254		Position loop integral gain
53	0x35	Undefined	1	-	RW	-	-
54	0x36	Undefined	1	-	RW	-	-
55	0x37	Lock Flag	1	1	RW	0 ~ 1		0: Disable lock (saved after power-off); 1: Enable lock

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	Bit15 is direction
58	0x3A	Present Speed	2	-	R	-	0.732 RPM	Bit15 is direction
60	0x3C	Present Load	2	-	R	-	0.1%	PWM duty cycle, Bit10 direction
62	0x3E	Present Voltage	1	-	R	-	0.1V
63	0x3F	Present Temperature	1	-	R	-	°C
64	0x40	Async Write Flag	1	0	R	-		Used in async write
65	0x41	Servo Status	1	0	R	-		Bit flags indicate errors
66	0x42	Moving Flag	1	0	R	-		BIT0: moving; BIT1: reached target
67	0x43	Target Position	2	-	R	-	0.087 degrees
69	0x45	Present Current	2	-	R	-	6.5mA	Phase current
71	0x47	Undefined	2	-	R	-	-
73	0x49	Current Offset	2	-	R	-	-	Zero offset

2.5 Factory Parameters

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
77	0x4D	vFk(*10)	1	–	R	–	–	Internal factory parameter (scaled ×10), used for velocity/feedback compensation
78	0x4E	vKgI	1	–	R	–	–	Internal velocity loop integral-related gain parameter
79	0x4F	pFk(*10)	1	–	R	–	–	Internal position-related factory parameter (scaled ×10)
80	0x50	Motion Speed Threshold	1	–	R	–	–	Threshold for determining whether the servo is in motion
81	0x51	DTs (ms)	1	–	R	–	ms	Control cycle timing parameter
82	0x52	eFk(*10)	1	–	R	–	–	Error/estimation compensation factor (scaled ×10)
83	0x53	Vk (ms)	1	–	R	–	ms	Internal timing constant for velocity control
84	0x54	Maximum Speed Limit	1	–	R	–	–	Factory-defined maximum allowable speed
85	0x55	Acceleration Limit	1	–	R	–	–	Factory-defined maximum acceleration limit
86	0x56	Acceleration Multiplier	1	–	R	–	–	Scaling factor for acceleration behavior

3. Special Byte Description

3.1 Servo Phase

Bit number / bit weight: description

BIT0 (1): servo phase (firmware version <= 3.41), magnetic encoder support (0: AS5600, 1: MT6701, firmware version >= 3.44)
BIT1 (2): current feedback direction phase; (0) forward, (1) reverse
BIT2 (4): driver bridge direction phase; (0) forward, (1) reverse
BIT3 (8): speed direction phase (firmware version <= 3.41)
BIT4 (16): angle feedback mode; (0) single-turn angle feedback, (1) multi-turn angle feedback
BIT5 (32): driver bridge configuration, (0) independent H-bridge, (1) integrated H-bridge
BIT6 (64): PWM frequency, (0) 24kHz, (1) 16kHz
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 + 4 + 2 = 134.

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): ----
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): ----
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 unload condition value is 4 + 1 = 5.

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FEETECH HLS 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