FEETECH SCS15 Bus Smart Control Servo

Product Specifications

• Product Name: Feetech Serial Bus Smart Control Servo
• Communication Protocol: Serial Bus Intelligent
• Series Compatibility: SCS and SMS series of servos
• SCS Series:
  • Communication: TTL level, single bus
  • Physical Connection: Three lines (two positive and negative poles of power supply)
• SMS Series:
  • Main Control Core: ARM 32-bit single-chip computer
  • Position Induction: 360-degree 12-bit precision magnet induction angle scheme
  • Communication Level: RS-485 mode

Product Usage Instructions

Communication Protocol Overview:
The Feetech Serial Bus Smart Control Servo communication protocol is designed for SCS and SMS series servos. Each servo in the network is assigned a unique ID number for communication.

Instruction Packet Format:
The instruction packet consists of the following components:

• Initial: 0XFF 0XFF indicating the start of a data packet
• ID No.: Unique ID number for each servo (0 to 253)
• Broadcast ID: ID No. 254 for broadcast instructions
• Data Length: Parameter count + 2
• Instruction: Operating Function Code
• Parameters: Additional control information, supporting up to two-byte parameters

Communication Mode:
The communication mode is serial asynchronous with a frame structure of start bit, data bits, and stop bit. Parity bits are not used, totaling 10 bits.

Memory Table Usage:
For parameters represented by two bytes, the SCS series and SMS series have different byte order conventions. Refer to the specific model’s memory table for actual control functions.

Serial Bus Smart Control Servo Communication Protocol Manual

Revision history

Summary of Communication Protocol

• The communication protocol of the FEETECH Serial Bus Intelligent servo is mainly applicable to FEETECH SCS and SMS series of servos. SCS series servo adopts TTL level and single bus (a signal line time-sharing multiplexing transmission and receiving data signal) communication connection, physical connection is three lines, including two positive and negative poles of power supply. The
• SMS series servo adopts an ARM 32-bit single-chip computer as the main control core, and position induction adopts a 360-degree 112-bit precision magnet induction angle scheme. The communication adopts RS-485 mode with strong anti-jamming ability. The communication still adopts asynchronous duplex, and the sending and receiving signals are processed asynchronously.
• Question-and-answer communication is adopted between the controller and the servo. The controller sends out the instruction package, and the servo returns to the response package.
• Multiple servos are allowed in a bus control network, so each servo is assigned a unique ID number in the network. The control command issued by the controller contains ID information. Only the servo matching the ID number can receive the command completely and return the response information.
• The communication mode is serial asynchronous. A frame of data is divided into 1 1-bit start bit, 8 8-bit data bits, and 1-bit stop bit. There are no parity bits; a total of 10 bits.
• The difference between the SCS series and the SMS series communication protocols is that two bytes represent the high byte and the low byte, respectively, when some parameters of the memory table are in the range of two bytes. Among them, the parameters of the SCS series are in the address of the memory table after the high byte and the low byte after the high byte, while the SMS series is in the low byte after the high byte. In addition, each servo has slightly different functions, so the actual control should refer to the memory table of the specific model.

Instruction packet

Instruction package format：

Initial： Continuous receipt of two 0XFFs indicating the arrival of data packets。

• ID No. Each servo has an ID number. ID number ranges from 0 to 253, converted to hexadecimal 0X00~0XFD。
• Broadcast ID: ID No. 254 is a broadcast ID. If the ID number issued by the controller is 254 (0XFE), all the Servos receive instructions, and no response information is returned except PING instructions (multiple servos can not use roadcast PING instructions on the bus).
• Data length: equal to the parameter N to be sent plus 2, that is, “N + 2″。
• Instruction: Packet Operating Function Code, see Instruction Type 1.3。

PARAMETERS:

• In addition to the additional control information required by the instructions, the parameters support a maximum of two-byte parameters to represent a memory value. The byte order refers to the manual memory control table for servo usage (different types of servos have different byte orders).
• Check sum: Check sum and Check Sum, the calculation method is as follows: Check Sum = ~ (ID + Length + Instruction + Parameter1 + … Parameter N). If the sum in parentheses exceeds 255, the lowest byte will be taken, and “~” means reverse.

Reply Packet
Reply packet is the servo’s reply to the controller.  Reply packet format is below:

• The returned response package contains the current status ERROR of the servo.
• If the current status of the servo is not normal, it will be reflected through this byte (the meaning of each status is detailed in the manual memory control table). If ERROR is 0, the servo will have no error information.
• If the instruction is a read instruction (READ DATA), then Parameter 1… Parameter N is the read information.

Instruction type
The following instructions are available for Feetech Serial Bus Intelligent servo Communication Protocol：

1Query status instruction PING

• Function: Read the working state of the servo
• Length 0X02
• Instruction 0X01
• Parameter no
• The PING command uses the broadcast address, and the steering gear also returns the response information.

Example 1 reads the working state of the steering gear with ID number 1

• Instruction frame: FF FF 01 02 01 FB `(sent in hexadecimal)

Data frame returned: FF FF 01 02 00 FC (hexadecimal display)

READ DATA
Function reads data from the servo memory control table

• Length * 0X04
• Instruction 0X02
• Parameter 1. Head address of the read-out segment of data
• Parameter 2. Length of read data
• Example 2: Read the current position of the servo with ID 1 (low byte before, high byte after).
• Two bytes are read from address 0X38 in the control table. Instruction frame: FF FF 01 04 02 38 02 BE (sent in hexadecimal)

Data frame returned: FF FF 01 04 00 18 05 DD (hexadecimal display)

Read out two byte data: low byte L 0X18 high byte H 0X05

• Two-byte synthesis of 16-bit data 0X0518, using decimal representation of the current location of 1304.

WRITE DATA

• Function. Write data to the servo memory control table
• Length N+3 (N is the parameter length)
• Instruction 0X03
• Parameter 1. Head address ofthe  the data write segment
• Parameter 2: The first data written
• Parameter 3. Second data
• Parameter N+1 Number N Data
• Example 3 sets an ID of any number to 1.
• The address ofthe  ID number is 5 in the control table, so write 1 at address 5. The ID of the sending instruction package uses the broadcast ID (0xFE).
• Instruction frame: FF FF FE 04 03 05 01 F4 (sent in hexadecimal)

Because broadcasting ID is used to send instructions, there will be no data return. In addition, the memory table EPROM has a protective lock switch, which needs to be turned off before modifying the ID; otherwise, the sample ID number will not be saved when the power is off. For detailed operation, please refer to the memory table or operation manual of the specific steering gear type.

Example 4 controls the ID1 servo to rotate to 2048 at a speed of 1000 seconds.

In the control table, the first address of the target location is 0X2A, so six consecutive bytes of data are written at the address 0X2A, namely position data 0X0800 (2048), time data 0X0000 (0), speed data 0X03E8 (1000). The ID of the sending instruction package uses a non-broadcast ID (0xFE), so the servo will return to the status package when the instruction is received.

Instruction frame: FF FF 01 09 03 2A 00 08 00 E8 03 D5 (sent in hexadecimal)

Instruction frame: FF FF 01 09 03 2A 00 08 00 E8 03 D5 (sent in hexadecimal)

Data frame returned: FF FF 01 02 00 FC (hexadecimal display）

• 0XFF 0XFF 0X01 0X02 0X00 0XFC

The return working state is 0, indicating that the servo has received the instructions correctly and correctly and has begun to execute them.

REG WRITE
The REG WRITE instruction is similar to the WRITE DATA except that the execution time is different. When the REG WRITE instruction frame is received, the received data is stored in the buffer reserve, and the Registered Instruction Register is set to 1. When the ACTION instruction is received, the stored instruction is finally executed.

• Length N+3 (N is the number of data to be written)
• Instruction 0X04
• Parameter 1. The header address of the area where the data is to be written, Parameter 2. The first data to be written
• Parameter 3. The second data to be written
• Parameter N+:1 The Nth Data to Write
• Example: 5 Control ID1 to ID10 servo to rotate to 2048 position at 1000 per second. Onthe only ID in the following instruction package receives instructions on the bus and returns. Other ID numbers are not returned on the bus.。
• ID 1 Asynchronous Write Instruction Pack： FF FF 01 09 04 2A 00 08 00 00 E8 03 D4 ID 1 Return Pack： FF FF 01 02 00 FC
• ID 2 Asynchronous Write Instruction Pack：  FF FF 02 09 04 2A 00 08 00 00 E8 03 D3 ID 3 Asynchronous Write Instruction Pack： FF FF 03 09 04 2A 00 08 00 00 E8 03 D2 ID 4 Asynchronous Write Instruction Pack： FF FF 04 09
• 04 2A 00 08 00 00 E8 03 D1 ID 5 Asynchronous Write Instruction Pack： FF FF 05 09 04 2A 00 08 00 00 E8 03 D0 ID 6 Asynchronous Write Instruction Pack： FF FF 06 09 04 2A 00 08 00 00 E8 03 CF ID 7 Asynchronous Write
• Instruction Pack： FF FF 07 09 04 2A 00 08 00 00 E8 03 CE ID 8 Asynchronous Write Instruction Pack： FF FF 08 09 04 2A 00 08 00 00 E8 03 CD ID 9 Asynchronous Write Instruction Pack： FF FF 09 09 04 2A 00 08 00 00 E8 03
• CC ID10 Asynchronous Write Instruction  Pack：FF FF 0A 09 04 2A 00 08 00 00 E8 03 CB

Executing Asynchronous Write Instruction ACTION

Function trigger REG WRITE instruction

• Length 0X02
• Instruction 0X05
• Parameter no

ACTION instruction is very useful for controlling multiple servos at the same time.

• When controlling multiple servos, the ACTION command enables the first and last servos to perform their respective actions simultaneously without delay.
• When the action command is sent to multiple servos, the broadcast ID (0xFE) is used, so no data frame will be returned when the command is sent.
• Example 6: After issuing the asynchronous writing instructions that control ID1 to ID10servoso t,o rotate the 2048 position at a speed of 1000 seconds, the following instruction packages (FF FF FE 02 05 FA) need to be sent when the asynchronous writing instructions need to be executed. All servos on the bus receive this instruction
  and run the asynchronous writing instruction received before.

SYNC WRITE

• Function used to control multiple servos
• ID 0XFE
• Length (L + 1) * N + 4 (L: Length of data sent to each servo, N: Servo Number)
• Instruction 0X83
• Parameter 1:  Head address of write data
• Parameter 2 Length of write data(L)
• Parameter 3 First servo Number
• Parameter 4 Write the first data of the first servo
• Parameter 5 Write the L data of the first servo
• Parameter L+3 Write the second data of the first servo Parameter L+4
• The second Servo ID number
• Parameter L+5 Write the first data of the second servo
• Parameter L+6 Write the second data of the second servo
• Parameter 2L+4 Write the L data of the second servo
• Unlike the REG WRITE + ACTION instruction, the real-time performance is higher. A SYNC WRITE instruction can modify the control table contents of multiple servos at one time, while the REG WRITE + ACTION instruction can be implemented step by step.
• Nevertheless, when using SYNC WRITE instructions, the length of the data written must be the same as the first address of the data saved.
• Example 77 Writing position 0X0800, time 0X000,0 and speed 0X03E8 for ID1-ID4 with four servo header addresses 0X2A (low byte in front, high node in back)

Instruction free: FF FF FE 20 83 2A 06 01 00 08 00 00 E8 03 02 00 08 00 00 E8 03 03 00 08 00 00 E8 03 04 00 08 00 00 E8 03 58 (Send in hexadecimal)

Because broadcasting ID is used to send instructions, no data is returned.。

RESET Instruction

• Function:n Reset the specific data in the memory control table (specific Servo type is used)
• length 0X02
• Instruction 0X06
• Parameter NO
• For example, le rest et servo， ID number is 0。
• Instruction frame FF 01 02 06 F6 (Send in hexadecimal)

Returned data frame： FF FF 01 02 00 FC （Send in hexadecimal）

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FAQs

Documents / Resources

FEETECH SCS15 Bus Smart Control Servo [pdf] Instruction Manual SCS15 Bus Smart Control Servo, SCS15, Bus Smart Control Servo, Smart Control Servo, Control Servo

References

• User Manual