FEETECH SMS Servo Memory Table Analysis

FEETECH SMS Servo – Memory Table Analysis

Magnetic Encoder SMS Servo

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1. Servo Communication Protocol

The servo uses the FT-SCS custom protocol. The default serial port configuration at the factory is as follows: the baud rate of the SMS servo is 115200 by default, and it uses RS485 bus communication.

The configurable baud rate range is 38400 to 1 Mbps. The default communication address (station number) 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 respectively represent the following baud rates: 1000000 (0), 500000 (1), 250000 (2), 128000 (3), 115200 (4), 76800 (5), 57600 (6), 38400 (7).
7	0x07	Response Return Delay	1	0	RW	0/50 ~ 253	2us	The maximum configurable return delay is 254 × 2 = 508 μs. 0 indicates the minimum return delay. If the setting is below 50, it defaults to 50 (100 μs).
8	0x08	Response Status Level	1	1	RW	0 ~ 1		0: No response packet is returned for any instruction except read instructions and PING instructions. 1: A response packet is returned for all instructions.
9	0x09	Minimum Angle Limit	2	0	RW	0 ~ 4094	0.087 degrees	This value is 0 when multi-turn absolute position control is used.
11	0x0B	Maximum Angle Limit	2	4095	RW	1 ~ 4095	0.087 degrees	This value is 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	1000	RW	0 ~ 1000	0.1%	Torque limit is assigned to address 48 at power-on.
18	0x12	Phase	1	-	RW	0 ~ 254		Special function byte. Do not modify unless specifically required.
19	0x13	Unload Condition	1	-	RW	0 ~ 254		Setting the corresponding bit to 1 enables the respective protection, and setting it to 0 disables the respective protection.
20	0x14	LED Alarm Condition	1	-	RW	0 ~ 254		Setting the corresponding bit to 1 enables the flashing alarm, and setting it to 0 disables the flashing alarm.
21	0x15	Position Loop Proportional Gain (Kp)	1	-	RW	0 ~ 254		Proportional gain for motor control (1/4)
22	0x16	Position Loop Derivative Gain (Kd)	1	-	RW	0 ~ 254		Derivative gain for motor control (1/8)
23	0x17	Position Loop Integral Gain (Ki)	1	0	RW	0 ~ 254		Integral gain for motor control
24	0x18	Minimum Starting Force	1	-	RW	0 ~ 254	0.1%	Set the minimum starting torque of the servo
25	0x19	Integral Limit Value	1	0	RW	0 ~ 254		Maximum integral value = Integral limit value × 4. 0 disables the integral limit function. This setting takes effect in position mode 0 and mode 4.
26	0x1A	Positive Dead Zone	1	1	RW	0 ~ 16	0.087 degrees	The minimum unit is one minimum resolvable angle.
27	0x1B	Negative Dead Zone	1	1	RW	0 ~ 16	0.087 degrees	The minimum unit is one minimum resolvable angle.
28	0x1C	Protection Current	2	511	RW	0 ~ 2047	6.5mA	The maximum configurable current is 500 × 6.5 mA = 3250 mA.
30	0x1E	Angular Resolution	1	1	RW	1 ~ 128		Amplification Factor of the Sensor’s Minimum Resolvable Angle
31	0x1F	Position Offset	2	0	RW	0 ~ 8191	0.087 degrees	0 to 2047 represent 0 to 2047; 2048 to 4095 represent 0 to -2047; 4096 to 6143 represent 2048 to 4095; 6144 to 8191 represent -2048 to -4095.
33	0x21	Operating Mode	1	0	RW	0 ~ 2		0: Position servo mode; 1: Constant speed mode; 2: PWM open-loop speed control mode; 3: Step mode
34	0x22	Holding Torque	1	20	RW	0 ~ 254	1%	The torque output after entering overload protection. For example, a setting of 20 means 20% of the maximum torque.
35	0x23	Protection Time	1	200	RW	0 ~ 254	10ms	The duration for which the current load output exceeds the overload torque is timed. For example, a setting of 200 means 2 seconds. The maximum configurable time is 2.5 seconds.
36	0x24	Overload Torque	1	80	RW	0 ~ 254	1%	The maximum torque threshold that starts the overload protection timing. For example, a setting of 80 means 80% of the maximum torque.
37	0x25	Velocity Closed-Loop Proportional Gain (Kp)	1	-	RW	0 ~ 254		Velocity loop proportional gain in constant speed mode (Mode 1)
38	0x26	Overcurrent Protection Time	1	200	RW	0 ~ 254	10ms	The maximum configurable time is 254 × 10 ms = 2540 ms.
39	0x27	Velocity Closed-Loop Integral Gain (Ki)	1	-	RW	0 ~ 254		Velocity loop integral gain 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	-	Write 0: Disable torque output; write 1: Enable torque output; write 128: Calibrate any current position to 2048.
41	0x29	Acceleration	1	0	RW	0 ~ 254	8.7°/s²	Servo acceleration/deceleration. 0 indicates maximum acceleration.
42	0x2A	Target Position	2	0	RW	-32767 ~ 32767	0.087 degrees	Absolute position control mode. The maximum value corresponds to the maximum effective angle. Bit 15 is the direction bit.
44	0x2C	PWM Open-Loop Speed	2	1000	RW	0~1000	0.1%	Effective in PWM open-loop speed control mode. Bit 10 is the direction bit.
46	0x2E	Operating Speed	2	Default maximum speed of the servo at the factory	RW	-32767 ~ 32767	0.732RPM/0.0146RPM	Sets the maximum operating speed of the motor. Bit 15 is the direction bit. A speed value of 0 defaults to the maximum speed, while a setting of 0 via the phase configuration means stop. The speed unit can be configured via the phase setting, offering two options: 0.732 RPM or 0.0146 RPM. When the speed unit is set to 0.0146 RPM, its precision remains 0.732 RPM.
48	0x30	Torque Limit	2	Maximum torque (16). Default value: 1000.	RW	0 ~ 1000	0.1%	The user can programmatically modify this value to control the stall torque output.
50~54	0x32~0x36	Undefined	1	-	-	-	-	-
55	0x37	Lock Flag	1	1	RW	0 ~ 1	-	Write 0 to disable the write lock. Values written to EPROM addresses are saved after power-off. Write 1 to enable the write lock. Values written to EPROM addresses are 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	Current Position	2	-	RO	0 ~ 2	0.087 degrees	Feedback of the servo’s current absolute position. Bit 15 is the direction bit. In step mode (Mode 3), the step difference between the current position and the target position is returned. Bit 15 is the direction bit.
58	0x3A	Current Speed	2	-	RO	0 ~ 254	0.732RPM/0.0146RPM	Feedback of the current motor speed. The speed unit is configured via the phase setting. Bit 15 is the direction bit.
60	0x3C	Current Load	2	-	RO	-32767 ~ 32767	0.1%	The current voltage duty cycle controlling the motor drive output. Bit 10 is the direction bit.
62	0x3E	Current Voltage	1	-	RO	0~1000	0.1V	Current Servo Operating Voltage
63	0x3F	Current Temperature	1	-	RO	-32767 ~ 32767	°C	Current Internal Operating Temperature of the Servo
64	0x40	Asynchronous Write Flag	1	0	RO	0 ~ 1000	-	Flag bit when using asynchronous write commands
65	0x41	Servo Status	1	0	RO	-	-	When the corresponding bit is set to 1, it indicates that the respective error has occurred.
66	0x42	Movement Flag	1	0	RO	0 ~ 1	-	The flag is 1 when the servo is moving, and 0 when the servo has reached the target and stopped. The flag remains 0 when the target position is not updated.
67	0x43	Target Position	2	0	RO	-	0.087 degrees	Current Target Position
69	0x45	Current Current	2	-	RO	-	6.5mA	Feedback of the current motor phase current
71	0x47	Undefined	2	-	RO	-	-

3.5 Factory Parameters

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
80	0x50	Movement Speed Threshold	1	-	RO	-	-
81	0x51	DTs(ms)	1	-	RO	-	-
82	0x52	Speed Unit Factor	1	-	RO	-	-
83	0x53	Hts(ns)	1	-	RO	-	-	20.83 ns. Valid for SMS servo firmware version 2.54 or higher. For other versions, keep it at 0.
84	0x54	Maximum Speed Limit	1	-	RO	-	-	Unit: 0.732 rpm
85	0x55	Acceleration Limit	1	-	RO	-	-
86	0x56	Acceleration Multiplier	1	-	RO	-	-	When the acceleration is 0, the acceleration multiplier takes effect. If both the acceleration and the acceleration multiplier are 0, the servo responds at the fastest speed.

3. Special Byte Description

3.1 Servo Phase

Bit Count / Bit Weight Description

Bit 0 (1): Driver direction phase. (0) forward, (1) reverse.
BIT1 (2): Bridge mode — 0 = brushless, 1 = brushed (restart)
BIT2 (4): Speed unit — 0 = 0.732 RPM, 1 = 0.0146 RPM
BIT3 (8): Speed mode — 0 = speed 0 = stop, 1 = speed 0 = max
BIT4 (16): Angle feedback — 0 = single-turn, 1 = full angle
BIT5 (32): Voltage sampling — 0 = 1.5K low, 1 = 1K high
BIT6 (64): PWM frequency — 0 = 24 kHz, 1 = 16 kHz
BIT7 (128): Position feedback direction — 0 = forward, 1 = reverse

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

For example: if the original phase value is 0 and the servo is set to run in reverse, the phase value becomes 128 + 1 = 129.

3.2 Servo Status

Servo status: 0 indicates normal, 1 indicates abnormal.

Bit Count / Bit Weight Description

BIT0 (1): Voltage status
BIT1 (2): Magnetic encoder status
BIT2 (4): Temperature status
BIT3 (8): Current status
BIT4 (16): Reserved
BIT5 (32): Load status
BIT6 (64): Reserved
BIT7 (128): Reserved

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Note: Multiple statuses can be combined. The servo status value is the sum of the bit values of all active statuses.

Example: Overvoltage/undervoltage (1) + Overheating (4) = 5.

3.3 Unload Condition

Unload condition — 0 = disabled, 1 = enabled

Bit Count / Bit Weight Description

BIT0 (1): Voltage protection
BIT1 (2): Magnetic encoder protection
BIT2 (4): Over-temperature protection
BIT3 (8): Overcurrent protection
BIT4 (16): Reserved
BIT5 (32): Load overload
BIT6 (64): Reserved
BIT7 (128): Reserved

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Note: Multiple protection conditions can be combined. The unload condition value is the sum of the bit values of all enabled protections.

Example: Voltage protection (1) + Over-temperature protection (4) = 5.

3.4 LED Alarm Condition

LED alarm condition — 0 = disabled, 1 = enabled

Bit Count / Bit Weight Description

BIT0 (1): Voltage alarm
BIT1 (2): Magnetic encoder alarm
BIT2 (4): Over-temperature alarm
BIT3 (8): Overcurrent alarm
BIT4 (16): Reserved
BIT5 (32): Load overload alarm
BIT6 (64): Reserved
BIT7 (128): Reserved

💡

Note: Multiple alarm conditions can be combined. The LED alarm condition value is the sum of the bit values of all enabled alarms.

Example: Voltage alarm (1) + Over-temperature alarm (4) = 5.

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FEETECH SMS 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
3.5 Factory Parameters
3. Special Byte Description
3.1 Servo Phase
3.2 Servo Status
3.3 Unload Condition
3.4 LED Alarm Condition