Hardware

What to connect between your MCU and DYNAMIXEL X-series servos, with which bus settings, and the traps of a half-duplex line.

All values here come from the ROBOTIS e-Manual pages for the XC430-W150, the XM430-W350 and Protocol 2.0. Other X-series models differ in supply range and in some control-table units: check the e-Manual page of your model.

Connectors

The bus is multidrop: every servo shares GND, VDD and DATA, and each answers only to its own ID.

Pin	TTL (3-pin)	RS-485 (4-pin)
1	GND	GND
2	VDD (servo supply)	VDD (servo supply)
3	DATA	DATA+
4		DATA-

Housings are JST EHR-03 (TTL) and EHR-04 (RS-485), with SEH-001T-P0.6 crimp terminals. The XC430-W150 is TTL only; the XM430-W350 comes in a TTL and an RS-485 version.

Half-duplex wiring

TTL DATA is one wire that carries both directions, so the MCU's TX and RX must take turns. The transport you write handles the turn-around; the driver never touches a pin. Three wirings work:

Wiring	Turn-around in the transport	EchoPolicy
Buffer or RS-485 transceiver with a DIR pin	DIR on to send, off in finish_transmit()	None
Auto-direction transceiver	None	None
TX and RX joined, open drain	None; RX hears TX and the driver drops it	ExpectedLocalEcho

ROBOTIS's reference TTL circuit is designed for a 5 V or 5 V tolerant MCU and says to use a level shifter otherwise. On a 3.3 V MCU such as the ESP32, put a buffer or level shifter rated for both levels between the UART and DATA. A transistor TTL adapter is fine for bench reads at 57600 bit/s; qualify a proper buffer before high baud rates or long cables.

RS-485 needs a transceiver with DATA+ and DATA- to pins 3 and 4, and a direction pin unless it switches automatically.

Bus settings

Setting	Value
Format	8 data bits, no parity, 1 stop bit, asynchronous
Speed	9600, 57600, 115200 bit/s, 1, 2, 3, 4 or 4.5 Mbit/s (Baud Rate, address 8, index 0 to 7)
Factory setting	57600 bit/s (index 1), ID 1
IDs	0 to 252; 254 (0xFE) is broadcast
Reply delay	Return Delay Time (address 9), 2 µs per unit; factory value 250 (500 µs)

The host and every servo on the bus must use the same rate. Change a servo's rate with a register write, then follow it with Bus::SetHostBaudRate() (API guide).

Protocol 2.0

The host sends an instruction packet and, unless it was broadcast, the addressed servo answers with a status packet. Every multi-byte field is little-endian.

Field	Instruction packet	Status packet
Header, reserved	FF FF FD 00	FF FF FD 00
ID	Target servo, or FE	Answering servo
Length (2 bytes)	Parameters + 3	Parameters + 4
Instruction	Ping 01, Read 02, Write 03, Sync Read 82, Sync Write 83	55
Error		Bit 7: hardware alert; bits 0 to 6: error number
Parameters, CRC-16	Address and data	Data

sequenceDiagram
    participant H as Host (driver)
    participant S as Servo ID 1
    H->>S: Read, address 132, 4 bytes
    Note over H: finish_transmit(), release the line
    Note over S: Return Delay Time (500 µs factory)
    S-->>H: Status, error 0, 4 data bytes

The same exchange on the wire, reading Present Position:

host  -> FF FF FD 00  01  07 00  02  84 00 04 00        CRC_L CRC_H
servo -> FF FF FD 00  01  08 00  55  00  p0 p1 p2 p3   CRC_L CRC_H
         header       ID  length  inst err/params

The SDK builds and checks these packets; the driver turns a missing or corrupt status into Timeout or ChecksumError and the error byte into DeviceError.

Power

Model	Supply (V)	Recommended (V)
XC430-W150	6.5 to 14.8	12.0
XM430-W350	10.0 to 14.8	12.0

The servos do not run from 3.3 V or 5 V. Feed pin 2 from a supply sized for the stall current of every servo on the bus (1.4 A for one XC430-W150 at 12 V), join its ground to the MCU's and keep the logic path between them level-compatible. Present Input Voltage (address 144, 0.1 V per unit) reads the supply at each servo.

Control table used by the driver

The driver's X-series descriptor (inc/dynamixel_model.hpp) uses these addresses. EEPROM entries can only be written while torque is off.

Address	Name	Bytes, area
0	Model Number	2, EEPROM
6, 7, 8	Firmware Version, ID, Baud Rate	1 each, EEPROM
11	Operating Mode	1, EEPROM
64	Torque Enable	1, RAM
70	Hardware Error Status	1, RAM
100, 102, 104	Goal PWM, Goal Current, Goal Velocity	2, 2, 4, RAM
108, 112	Profile Acceleration, Profile Velocity	4 each, RAM
116	Goal Position	4, RAM
124, 126	Present PWM, Present Load or Current	2 each, RAM
128, 132	Present Velocity, Present Position	4 each, RAM
144, 146	Present Input Voltage, Present Temperature	2, 1, RAM

Units on the XC430-W150: position 1 pulse (4096 per revolution, 0.088°), velocity 0.229 rev/min, PWM 0.113 %, load 0.1 %. On XM and XH models address 126 is Present Current, 2.69 mA per unit on the XM430-W350.

Example boards

The ESP32 examples run on an ESP32-C6 or ESP32-S3 with UART1:

MCU	TX	RX
ESP32-C6	GPIO4	GPIO5
ESP32-S3	GPIO17	GPIO18

The pins, an optional direction GPIO and the baud rate are Kconfig options (Kconfig.projbuild).

Reference documents

Document	What it is for
XC430-W150 e-Manual	The first validated servo: specifications, control table, connector
XM430-W350 e-Manual	A current-capable model, TTL and RS-485
Protocol 2.0	Packet format, instructions, error byte
DYNAMIXEL SDK	The protocol engine the driver wraps