FEETECH SMSMB Servo – Memory Table Analysis

SMSMB Servo – Memory Table Analysis

Magnetic Encoder SMSMB Servo

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1. Servo Communication Protocol

The servo uses the MODBUS-RTU standard protocol. The factory default serial configuration is as follows: baud rate 115200, with 8 data bits, no parity, and 1 stop bit.

The baud rate is configurable from 9600 to 256 Kbps.

The default communication address (station ID) is 1.

2. Servo Memory Table Definition

2.1 Version Information

Address (DEC)	Address (HEX)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
0	0x00	Firmware Version Number	2	–	RO
1	0x01	Servo Version Number	2	–	RO
2	0x02	Firmware Release Year	2	–	RO
3	0x03	Firmware Release Month	2	–	RO

2.2 EPROM Configuration

Address (DEC)	Address (HEX)	Address (PLC)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
10	0x0A	40011	ID	2	1	RW	1 ~ 247	No.	Unique identification number on the bus; duplicate IDs are not allowed. Address 0 (0x00) is the broadcast ID
11	0x0B	40012	Baud Rate	2	2	RW	0 ~ 9		0–9 correspond to: 256000 (0), 128000 (1), 115200 (2), 57600 (3), 56000 (4), 38400 (5), 19200 (6), 14400 (7), 9600 (8), 4800 (9)
12	0x0C	40013	Response Delay	2	500	RW	0 ~ 500	1 µs	0 indicates minimum response delay; maximum is 500 µs
13	0x0D	40014	Minimum Angle Limit	2	0	RW	0 ~ 4095	0.0879 degrees	Minimum motion range limit; must be less than maximum angle limit; set to 0 in multi-turn absolute mode
14	0x0E	40015	Maximum Angle Limit	2	4095	RW	0 ~ 4095	0.0879 degrees	Maximum motion range limit; must be greater than minimum angle limit; set to 0 in multi-turn absolute mode
15	0x0F	40016	Position Calibration	2	0	RW	-2047 ~ 2047	0.0879 degrees	Calibration range; writing 4 via fault reset (134) calculates and stores mid-position (2048)
16	0x10	40017	Operating Mode	2	0	RW	0 ~ 4		0: Servo mode; 1: Constant speed mode; 2: Reserved; 3: Special mode (torque disabled at target); 4: Step mode
17	0x11	40018	Position Loop Proportional Gain	2	–	RW	0 ~ 254		Controls proportional gain of motor
18	0x12	40019	Position Loop Derivative Gain	2	–	RW	0 ~ 254		Controls derivative gain of motor
19	0x13	40020	Position Loop Integral Gain	2	0	RW	0 ~ 254		Controls integral gain of motor
20	0x14	40021	Speed Loop Proportional Gain	2	–	RW	0 ~ 254		Speed loop proportional gain in constant speed mode (Mode 1)
21	0x15	40022	Speed Loop Integral Gain	2	–	RW	0 ~ 254		Speed loop integral gain in constant speed mode (Mode 1)

2.3 SRAM Control

Address (DEC)	Address (HEX)	Address (PLC)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
128	0x80	40129	Target Position	2	0	RW	-32768 ~ 32767	0.0879 degrees	Absolute position control mode; maximum value corresponds to maximum valid angle
129	0x81	40130	Torque Switch	2	0	RW	0 ~ 1		0: Disable torque output; 1: Enable torque output
130	0x82	40131	Acceleration	2	Default acceleration value	RW	0 ~ 65535	8.79 degrees/s²	If set to 0, maximum acceleration is used; initialized from “Acceleration Default Value (405)” at power-on
131	0x83	40132	Operating Speed	2	Default speed value	RW	0 ~ 65535	0.732 RPM	Initialized from “Speed Default Value (406)” at power-on
132	0x84	40133	Torque Limit	2	Default torque limit	RW	0 ~ 1000	0.1 %	Initial value is loaded from torque limit default (0x194); user can modify to control maximum output torque; also affects speed linearly (reducing torque reduces no-load max speed)
133	0x85	40134	Lock Flag	2	1	RW	0 ~ 1 / 128		0: Disable EPROM write lock (values saved after power-off); 1: Enable write lock (values not saved after power-off); 128: Disable factory parameter write lock
134	0x86	40135	Fault Reset	2	0	RW	0 ~ 65535		Each bit resets corresponding fault when set to 1; after successful reset, the bit is cleared; see special byte definition for details

2.4 SRAM Feedback

Address (DEC)	Address (HEX)	Address (PLC)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
256	0x100	40257	Servo Status	2	0	RO	–		Bit=1 indicates corresponding error; see special byte definition
257	0x101	40258	Present Position	2	0	RO	–	0.0879 degrees	Feedback of current position; absolute position control mode, maximum value corresponds to maximum valid angle
258	0x102	40259	Present Speed	2	0	RO	–	0.732 RPM	Feedback of current motor speed
259	0x103	40260	Output PWM	2	0	RO	–	0.1 %	Current PWM duty cycle driving the motor
260	0x104	40261	Present Voltage	2	0	RO	–	0.1 V	Current operating voltage
261	0x105	40262	Present Temperature	2	0	RO	–	°C	Internal servo temperature
262	0x106	40263	Moving Flag	2	0	RO	–		1: moving; 0: stopped at target
263	0x107	40264	Present Current	2	0	RO	–	6.5 mA	Maximum measurable current: 500 × 6.5 mA = 3250 mA

2.5 Factory Parameters

Address (DEC)	Address (HEX)	Address (PLC)	Function Name	Number of Bytes	Initial Value	Access	Value Range	Unit	Description
384	0x180	40385	Motion Detection Threshold	2	–	Default	–		Servo factory default parameter
385	0x181	40386	D Control Time	2	–	Default	–		Servo factory default parameter
386	0x182	40387	Maximum Speed Limit	2	–	Default	0 ~ 32767	0.732 RPM	Servo factory default parameter
387	0x183	40388	H-Bridge Dead Time	2	–	Default	–		Servo factory default parameter
388	0x184	40389	Acceleration Limit	2	–	Default	0 ~ 65535	8.79 degrees/s²	Servo factory default parameter
389	0x185	40390	Startup Torque	2	–	Default	0 ~ 1000	0.1 %	Minimum output startup torque; 1000 = 100% stall torque
390	0x186	40391	Clockwise Dead Zone	2	–	Default	0 ~ 32	0.0879 degrees
391	0x187	40392	Counterclockwise Dead Zone	2	–	Default	0 ~ 32	0.0879 degrees
392	0x188	40393	Phase	2	–	Default	0 ~ 255		Special function byte; should not be modified unless necessary; see special byte definition
393	0x189	40394	Protection Switch	2	–	Default	0 ~ 255		Bit=1 enables corresponding protection; Bit=0 disables; see special byte definition
394	0x18A	40395	LED Alarm Condition	2	–	Default	0 ~ 255		Bit=1 enables LED alarm; Bit=0 disables; see special byte definition
395	0x18B	40396	Maximum Temperature Limit	2	–	Default	0 ~ 100	°C	Maximum operating temperature limit (e.g., 70°C)
396	0x18C	40397	Maximum Input Voltage	2	–	Default	Minimum input voltage ~ 360	0.1 V	e.g., 80 = 8.0 V
397	0x18D	40398	Minimum Input Voltage	2	–	Default	0 ~ Maximum input voltage	0.1 V	e.g., 40 = 4.0 V
398	0x18E	40400	Overload Current	2	–	Default	0 ~ 511	6.5 mA	Servo overload protection current
399	0x18F	40401	Overcurrent Protection Time	2	–	Default	0 ~ 5000	1 ms	Maximum duration exceeding overload current
400	0x190	40402	Protection Torque	2	–	Default	0 ~ 1000	0.1 %	Output torque during overload protection; e.g., 200 = 20%
401	0x191	40403	Overload Torque Threshold	2	–	Default	0 ~ 1000	0.1 %	Torque threshold to trigger overload protection
402	0x192	40404	Overload Protection Time	2	–	Default	0 ~ 5000	1 ms	Maximum time torque exceeds overload threshold
403	0x193	40405	Angular Resolution	2	1	Default	1 ~ 128		Amplification factor of minimum sensor resolution; affects control range
404	0x194	40406	Default Torque Limit	2	1000	Default	0 ~ 1000	0.1 %	Power-on default torque limit
405	0x195	40407	Default Acceleration	2	–	Default	0 ~ 65535	8.79 degrees/s²	Power-on default acceleration
406	0x196	40408	Default Speed	2	–	Default	0 ~ 32767	0.732 RPM	Power-on default 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): torque auto switch; (0) auto enable, (1) command enable, firmware >= 20.9
BIT3 (8): status auto reset; (0) auto reset, (1) command reset, firmware >= 20.9
BIT4 (16): angle feedback mode; (0) single-turn angle feedback, (1) full-range angle feedback
BIT5 (32): ----
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): torque status: 0 indicates torque off, 1 indicates torque on
BIT5 (32): load status

💡

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 Protection Switch

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

💡

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

LED 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

💡

Note:If multiple bits are set simultaneously, the LED 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.

3.5 Fault Reset

Fault reset: 0 invalid, 1 reset

Bit number / bit weight: description

BIT0 (1): reset overload fault; automatic reset enabled, reversing target position and disabling torque switch can also clear the fault
BIT1 (2): reset overcurrent fault; automatic reset enabled, reversing target position and disabling torque switch can also clear the fault
BIT2 (4): set midpoint; set current position to 2048 midpoint
BIT3 (8): ----
BIT4 (16): ----
BIT5 (32): reset overvoltage/undervoltage; when voltage returns to normal, write 32 to reset status; automatic reset enabled when voltage is normal
BIT6 (64): reset overheat status; when temperature returns to normal, write 64 to reset status; automatic reset enabled when temperature is normal
BIT7 (128): reset magnetic encoder status; when encoder is connected normally, write 128 to reset status; automatic reset enabled when encoder is normal

💡

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

For example: If overload fault reset and overcurrent fault reset are both triggered, the value is 1 + 2 = 3.

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SMSMB 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 Protection Switch
3.4 LED Alarm Condition
3.5 Fault Reset