xArm Controller RS-485 (Modbus RTU) User Guide

1. Overview

This manual describes the RS-485 communication capabilities of the UFACTORY xArm controller and how to use them under the Modbus RTU protocol.

The controller currently supports:

• Modbus RTU Master
• Modbus RTU Slave (Controller AC1310 or later, firmware V2.7.104 or later)

2. Modbus RTU Master

In Master mode, xArm actively communicates with external RS-485 slave devices.

2.1 Interface Definition

Terminal	Description	Note
M_A	RS-485 A / D+	Master
M_B	RS-485 B / D-	Master
GND	Signal Ground

2.2 Communication Parameters

Parameter	Default	Range
Baud Rate	2000000	4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600, 1000000, 1500000, 2000000, 2500000
Data Bits	8
Stop Bits	1	1, 2
Parity	None	None (N), Odd (O), Even (E)
Timeout	50 ms	1–9999 ms

2.3 Control Methods

2.3.1 UFACTORY Studio

RS-485 Port: Control Box Protocol: Modbus RTU
CRC will be appended automatically after the input command.

2.3.2 Python SDK

1. Set controller baud rate

arm.set_rs485_baudrate(200000, target='control_box')

2. Set timeout

arm.set_rs485_timeout(1000, target='control_box')

3. Send data

arm.set_rs485_data([0x08, 0x06, 0x01, 0x00, 0x00, 0x01], target='control_box')

3. Modbus RTU Slave

In Slave mode, xArm can be accessed by a PLC or host computer.

3.1 Interface Definition

Terminal	Description	Note
L_A	RS-485 A / D+	Slave
L_B	RS-485 B / D-	Slave
GND	Signal Ground

3.2 Communication Parameters

Parameter	Default	Range
Slave ID	1	1–247
Baud Rate	9600	4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, 921600, 1000000, 1500000, 2000000; (0-12)
Data Bits	8
Stop Bits	1	1, 2
Parity	None	None (N), Odd (O), Even (E); (0-2)

3.3 Parameter Configuration

Set parameters:

arm.set_modbusrtu_params(slave_id=1, baudrate=9600, stopbits=1, parity=0)

Get parameters:

arm.get_modbusrtu_params()

Example output:

(0, [1, 9600, 1, 0])

3.4 Register Mapping Examples

3.4.1 Function Code

• Discrete input register
  • 0x02: Read multiple discrete input registers
• Input register
  • 0x04: Read multiple input registers
• Coil register
  • 0x01: Read multiple coil registers
  • 0x05: Write single coil register
  • 0x0F: Write multiple coil registers
• Holding register
  • 0x03: Read multiple holding registers
  • 0x06: Write single holding register
  • 0x10: Write multiple holding registers
  • 0x16: Mask write single holding register
  • 0x17: Read and Write multiple holding registers

3.4.2 Status Registers (Read Only)

Discrete Input Registers (1 bit, READ only)

Address (Dec)	Address (Hex)	Description
0–31	0x00–0x1F	Controller digital input IO (16 valid)
32–39	0x20–0x27	Tool digital input IO (2 valid)
40–127	0x28–0x7F	Reserved

Input Registers (16 bit, READ only)

Address(Dec)	Address(Hex)	Description
0 ~ 1	0x00 ~ 0x01	32 controller Digital Inputs (Now only 16 effective)
2	0x02	8 tool Digital Inputs (Now only 2 effective)
3 ~ 6	0x03 ~ 0x06	4 controller analog inputs (now only 2 effective), it is 1000 times the real value
7 ~ 10	0x07 ~ 0x0A	4 tool analog inputs (now only 2 effective), it is 1000 times the real value
11 ~ 31	0x0B ~ 0x1F	Reserved
32	0x20	Robot Error code
33	0x21	Robot Warning code
34 ~ 35	0x22 ~ 0x23	Counter value (0x22 stores the higher 16-bit, 0x23 stores the lower 16-bit)
36 ~ 63	0x23 ~ 0x3F	Reserved
64 ~ 72	0x40 ~ 0x48	Current TCP coordinate of x/y/z/roll/pitch/yaw/rx/ry/rz values, register values are 10 times the real numbers (unit: mm, degree)
73 ~ 76	0x49 ~ 0x4C	TCP payload mass(1000x)/center_x(10x)/center_y(10x)/center_z(10x) (unit: kg, mm)
77 ~ 82	0x4D ~ 0x52	TCP Offset, register values are 10 times the real numbers(unit: mm, degree)
83 ~ 88	0x53 ~ 0x58	User/world coordinate offset, register values are 10 times the real numbers(unit: mm, degree)
89 ~ 95	0x59 ~ 0x5F	joint (J1-J7) angles, register values are 10 times the real numbers(unit: degree)
86 ~ 102	0x60 ~ 0x66	joint (J1-J7) temperature (unit: degree Celsius)
103 ~ 109	0x67 ~ 0x6D	joint (J1-J7) speed, register values are 10 times the real numbers(unit: degree/s)
110	0x6E	Robot TCP linear speed, register values are 10 times the real numbers(unit: mm/s)
111 ~ 127	0x6F ~ 0x7F	Reserved

3.4.3 Control Registers (Read / Write)

Coil Registers (1 bit, READ/WRITE)

Address(Dec)	Address(Hex)	Description
0 ~ 31	0x00 ~ 0x1F	32 controller Digital Output (Now only 16 effective)
32 ~ 39	0x20 ~ 0x27	8 tool Digital Output (Now only 2 effective)
40 ~ 127	0x28 ~ 0x7F	Reserved
128 ~ 134	0x80 ~ 0x86	joint (J1-J7) brake states
135 ~ 141	0x87 ~ 0x8D	joint (J1-J7) enable states
142	0x8E	Reduced mode (0: OFF, 1: ON)
143	0x8F	Digital Fence (0: OFF, 1: ON)
144	0x90	isPaused (0: False, 1: True)
145	0x91	isStopped (0: False, 1: True)
146 ~ 159	0x92 ~ 0x9F	Robot Mode (14 bits for mode 0-13 respectively, 0: not in this mode, 1: in this mode)
160 ~ 255	0xA0 ~ 0xFF	Reserved
256 ~ 511	0x100 ~ 0x1FF	General purpose, user defined

Holding Registers (16 bit, READ/WRITE)

Address (Dec)	Address (Hex)	Description
0-1	0x00-0x01	32 controller Digital Outputs (Now only 16 effective), each bit correspond to one IO in order
2	0x02	8 tool Digital Outputs (Now only 2 effective), each bit correspond to one IO in order
3-6	0x03-0x06	4 controller analog outputs (now only 2 effective), it is 1000 times the real value
7-10	0x07-0x0A	4 tool analog outputs (currently NOT EFFECTIVE), it is 1000 times the real value
11	0x0B	Modbus RTU slave ID
12	0x0C	Modbus RTU slave baud rate
13	0x0D	Modbus RTU slave stop bit
14	0x0E	Modbus RTU slave parity
15-31	0x0F-0x1F	Reserved
32	0x20	Robot Mode
33	0x21	Robot State
34-47	0x22-0x2F	Reserved
48-63	0x30-0x3F	Offline (Blockly) Task (only effective by writing multiple (max 16) holding registers to address 0x30 via function code 0x10, each register value correspond to one Blockly project with specific naming convention, for example: value 1 for project '00001', 12 for project '00012', projects will be executed automatically in order)
64	0x40	Gcode(Firmware≥2.4.0), trigged the gcode file under modbus_tcp folder.
65-255	0x41-0xFF	Reserved
256-511	0x100-0x1FF	General purpose, user defined