Development and use based on serial port protocol

Serial communication protocol

Document Purpose and Object

This document is applicable to the communication protocol for command/data interaction between any upper computer and the XGO series machine dog driver board. Used by advanced developers for secondary development of XGO.

Hardware Connection

Use a hex wrench to unscrew the two screws on the back, left and right, and two screws on the back. Remove the back panel of the machine dog and unplug the switch wire. The motherboard has two serial communication interfaces, which are connected to the upper computer wire sequence according to the motherboard screen printing wire sequence (TX to RX, RX to TX), and can then be debugged. The external power supply voltages of the two terminals are 5V and 3.3V respectively, and cannot be used simultaneously.

Software interface

Using standard TTL serial communication

BAUD	115200
Data bits	8
stop bit	1
Parity bit	no

Data Frame

The data frame adopts a fixed format: frame header+frame length+data+checksum+frame tail.

Header	Fixed to 0x55 0x00
frame length	Bytes of the entire data frame
data	Depending on the type of instruction, it has different meanings, as shown in Part 2
checksum	Add all bytes of length and data, take the lowest byte, and then invert it
End of Frame	Fixed to 0x00 0xAA

Instruct

It is recommended that the interval between each instruction on the upper computer should be at least 1ms to prevent packet loss caused by the machine dog not being able to process the instruction too quickly.

You can refer to [xgolib. py (24 KB)]（ https://www.elecfreaks.com/download/xgolib.py ）The code for send and read in.

Write instruction, no response (0x00)

Frame header	Frame length	Command type	First address	Data	Checksum	End of frame
0x55 0x00		0x00		data		0x00 0xAA

The write command will modify the data starting from the first address, and will not generate a response.

>For example, to modify the forward speed of the robot dog, the forward speed address is 0x30, and the maximum speed is forwarded, that is, the speed content is 0xFF. The specific instructions are as follows:
>0x55 0x00 0x09 0x00 0x30 0xFF 0xC7 0x00 0xAA
>The checksum calculation process is as follows:
>0x09+0x00+0x30+0xFF=0x138，Take the lowest byte 0x38, and get 0xC7 by inversion

Read command, response (0x02)

Frame header	Frame length	Command type	First address	Read length	Checksum	End of frame
0x55 0x00		0x02		uint_8		0x00 0xAA

The write command will read the data starting from the first address continuously, and no response will be generated.

The format of the returned data packet is:

Frame header	Frame length	Command type	First address	Date	Checksum	End of frame
0x55 0x00		0x12		data		0x00 0xAA

>For example, to read the angles of 12 servos, 0x50 is the address of the first servo position, 0x0C means to read 12 consecutively, the specific instructions are as follows：
>0x55 0x00 0x09 0x02 0x50 0x0C 0x98 0x00 0xAA
>The checksum calculation process is as follows:
>0x09+0x02+0x50+0x0C=0x67，Inverted to get 0x98
>read return packet:
>0x55 0x00 0x14 0x12 0x50 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x80 0x89 0x00 0xAA

Machine coordinate system

In the initial standing posture, the origin is directly below the fuselage, the forward direction of the robot dog is the positive direction of the X-axis, the left is the positive direction of the Y-axis, and the upward direction is the positive direction of the Z-axis.

Single leg coordinate system

The single-leg coordinate system is used to describe the position of the foot. The four legs correspond to four independent single-leg coordinate systems. The thigh joint is the origin. The forward direction of the robot dog is the positive direction of the x-axis, the left is the positive direction of the Y-axis, and the bottom is the positive direction of the Z-axis. Towards.

Servo number

	shoulder（3）	arm（2）	elbow（1）
left front leg (1）	13	12	11
right front leg（2）	23	22	21
right hind leg（3）	33	32	31
left hind leg（4）	43	42	41

Robot dog memory table

Adress	Function	read and write	initial value	Remark	model
0x00	working status	read	0x00		status information
0x01	battery power	read	0xff	The range is 0-100, linearly corresponding to the lowest value of power - the highest value
0x03	show mode	write	0x00	0x00 normal control mode |0x01 loop action
0x04	calibration mode	write	0x00	0x01 Enter the calibration mode 0x00 Exit the calibration mode and complete the calibration
0x05	update firmware	write	0x00	0x01 enters the update mode, the lower computer sends a same command as a reply, and after a delay of 1s, the upper computer starts to transmit hex
0x07	Firmware version	read		returns a 10-byte string
0x09	gait	write	0x00	0x00 TROT | 0x01 WALK | 0x02 HIGH WALK
0x20	Uninstall the servo	read and write	0x00	0x00 servo is in normal working state, 0x01 unloads all servos, 0x11-0x14 unloads legs 1-4 in sequence, 0x21-0x24 restores legs 1-4 in sequence	debug mode
0x21	Reset servo zero position	write	0x00	0x00 The steering gear is in normal working state 0x01 The current position of all steering gear records is zero. After this register is set to 0x01, it will automatically jump to 0x00
0x30	forward and backward moving speed	read and write	0x80	The range is 0x00-0xff, linearly corresponds to the reverse maximum value-forward maximum value, and the positive direction is based on the robot coordinate system, the same below (Note ③)	Machine mode
0x31	left and right movement speed	read and write	0x80
0x32	Clockwise rotation speed	read and write	0x80	Facing the direction of the z-axis, clockwise corresponds to the direction of the maximum value
0x33	body translation distance along the x direction	read and write	0x80	The point of contact between the foot and the ground remains unchanged but the body twists, the same below
0x34	body translation distance along the y direction	read and write	0x80
0x35	body height	read and write	0x80
0x36	Rotation angle of the body around the x-axis	read and write	0x80	Facing the coordinate axis, the direction clockwise corresponds to the maximum value direction, the same below
0x37	Rotation angle of the body around the y-axis	read and write	0x80
0x38	Rotation angle of the body around the z-axis	read and write	0x80
0x39	Rotate the body around the x-axis with a certain period	read and write	0x00	0x00 stops, 0x01-0xff linearly corresponds to the minimum-maximum rotation speed, this function and the direct setting of the position register cannot work at the same time
0x3A	Rotate the body around the y-axis with a certain period	read and write	0x00
0x3B	Rotate the body around the z-axis with a certain period	read and write	0x00
0x3C	No progress	read and write	0x00	0x00 stops, 0x01-0xff linearly corresponds to the minimum-maximum step height
0x3D	sports mode	read and write	0x00	0x00 Normal speed movement 0x01 Slow movement 0x02 High speed movement
0x3E	action command	write	0x00	For details, see the action instruction table. 255 is to restore the default posture. 1-N is each action (see the right side)
0x80	Translational movement along the X-axis direction with a certain period	read and write	0x00	0x00 stops, 0x01-0xff corresponds to the minimum-maximum rotation speed, and the movement range is half of the position limit
0x81	Translational movement along the Y-axis direction with a certain period	read and write	0x00
0x82	Translational movement along the Z-axis direction with a certain period	read and write	0x00
0x40	The position of the foot end of the left front leg in x direction	read and write	0x80	The range is 0x00-0xff, linearly corresponds to the reverse maximum value-forward maximum value, and the positive direction is based on the robot coordinate system, the same below	single leg mode
0x41	The position of the foot end of the left front leg in the y direction	read and write	0x80
0x42	The position of the foot end of the left front leg in z direction	read and write	0x80
0x43	The position of the foot end of the right front leg in x direction	read and write	0x80
0x44	The position of the foot end of the front leg in the y direction	read and write	0x80
0x45	The position of the foot end of the right front leg in z direction	read and write	0x80
0x46	Foot end position of right hind leg in x direction	read and write	0x80
0x47	The position of the foot end of the right hind leg in the y direction	read and write	0x80
0x48	The position of the foot end of the right hind leg in z direction	read and write	0x80
0x49	Foot position of left hind leg in x direction	read and write	0x80
0x4A	The position of the foot end of the left hind leg in the y direction	read and write	0x80
0x4B	The position of the foot end of the left hind leg in the z direction	read and write	0x80
0x50	ID is 11 servo position	read and write	0x80	The range is 0x00-0xff, linearly corresponding to the reverse maximum value - forward maximum value, the same below	Servo mode
0x51	ID is 12 servo position	read and write	0x80
0x52	ID is 13 servo position	read and write	0x80
0x53	ID is 21 servo position	read and write	0x80
0x54	ID is 22 servo position	read and write	0x80
0x55	ID is 23 servo position	read and write	0x80
0x56	ID is 31 servo position	read and write	0x80
0x57	ID is 32 servo position	read and write	0x80
0x58	ID is 33 servo position	read and write	0x80
0x59	ID is 41 servo position	read and write	0x80
0x5A	ID is 42 servo position	read and write	0x80
0x5B	ID is 43 servo position	read and write	0x80
0x5C	Set servo speed	read and write	0x80	The range is 0x00-0xff, linearly corresponding to min-max (valid only in this mode)
0x5D	ID is 52 servo position	read and write	0x80	Robotic Arm Forearm Servo
0x5E	ID is 53 servo position	read and write	0x80	Robotic Arm Big Arm Servo
0x61	IMU status	read and write	0x00	0x00 off 0x01 self-stabilizing mode
0x62	ROLL Angle	read
0x63	pitch angle	read
0x64	YAW angle	read
0x71	Gripper state	write	0x80	0x00-0xFF, 0x00 corresponds to the full opening of the jaws|0xFF corresponds to the full opening of the jaws
0x72	Arm Stabilization Mode	write	0x00	0x00 does not enable self-stabilization, 0x01 enables stabilization mode, and the position of the end of the robotic arm in space remains unchanged when the body is moving
0x73	Gripper X axis position	write	0x80	0x00-0xFF, corresponding to [-80mm, 155mm], the origin of the robot arm coordinate system is at the rotation axis of the arm servo
0x74	Gripper Z axis position	write	0x80	0x00-0xFF, corresponding to [-95mm, 155mm]

Action content

The action execution process can be interrupted by other commands, and no information will be sent to the host computer after the action execution is completed. If you want to automatically execute the next command after the action is completed, you can manually give a certain delay after sending the action command.

Action ID (decimal)	action content	execution time (seconds)
1	get down	3
2	stand up	3
3	creep forward	5
4	circle around	5
6	squat up	4
7	Turn Roll	4
8	Turn Pitch	4
9	Turn Yaw	4
10	three-axis rotation	7
11	pee	7
12	site down	5
13	wave	7
14	stretch	10
15	wave	6
16	swing left and right	6
17	Begging for food	4
18	looking for food	6
19	shake hands	10
20	chicken head	9
21	push ups	8
22	look around	7
23	dance	6
24	Naughty	7
128	Catch up	10
129	Caught	10
130	Catch	10
255	Restore default posture	1