README.md

Geeetech A30T Touch Screen

I got the information that the touch screen will not work together with the Marlin firmware. Although that is true for the time beeing I was able to build Marlin for my A30T and was also able to implement my own UI for the touch screen (ongoing, but will also show up on that branch). I really like to switch filaments or do the leveling via the touch screen, that is why I want to use the display. I also would like to avoid buying additional components or modify my complete printer by exchanging the board/display combination completely.

Unfortunately, the firmware of the touch screen is closed source, hence, I cannot analyze it by looking at the code. The (incomplete) Smartto code that is available from Geeetech via Github (here and here) does not explain much about the communication.

Hence, I want to analyze the communication between the touch screen board and the control board to be able to use it later on together with a version of Marlin.

General Information

The screen has it's own board (see picture) and is labeled as "Smartto_LCD 3.2 VER2.1 FR4 1.6mm 2019-10-31".

The main processor is an ARM chip labeled "STM32F103 VET6". This is the same processor as the main board has. After investing some time in analyzing the main board I'm pretty convinced that it is possible to install a custom firmware. Nevertheless, that would mean developing one basically from scratch, which will maybe be a good idea if I find some spare time (i.e. most likely never). Until then, I'll stick with the original firmware.

The connector labeled as J2 seems to be a serial connector as it is connected to the main board via that connector. There are 4 pins and on the main board the pins are labeled 5V, RX, TX and GND (see picture). The wires of the cable connecting the two ports are running straight. However, the connectors on each side are inverse to each other (see picture).

I bought three USB to TTL adapters (see picture) via the Internet to be able to connect to the touch screen and to also be able to connect to the control board and the touch screen concurrently to "listen in" on the communication that is happening. The adapters have an FT232RL chip, but actually I don't know whether this is really required. There are cheaper ones, but for about 10€ for all of them the price was OK for me. I use a break-out board that came with my Raspberry Pi to easily connect the adapter with the boards. The adapters are automatically recognized by my Linux Mint system and devices like /dev/ttyUSB0 are created.

In the Geeetech Smartto repository on Github I saw that a serial port is configured to use 115200 baud. I will use that for testing and see whether that works out OK.

In the following, many codes are postfixed with a star and a number, e.g. *92. I assume that these are some kind of check sum as they change based on the content of the message. I have to check on whether I can live without them or have to figure out what they do.

Approach

My approach to see what the communication pattern between the touch screen and the control board is as follows:

1. Connect the touch screen to Linux and see whether the display works at all. If this works out, check all the buttons on the screens and see what output they produce.
2. Connect the control board and the touch screen to the Linux system via two TTL devices. Forward all messages from one device to the other and also record the communication to see what messages are exchanged.
3. Send messages to the touch screen and the control board and see whether the "check sums" are required or not, and if they are, find out, how they can be derived.

Check 1: connect the touch screen to Linux

First, I unplug the cable from both boards. I connect the TTL adapter with the control board side of the cable. I connect the cables as they are described on the control board. Then, I use the Linux tool screen to connect to the TTL device and see what happens. The command I use is:

sudo screen /dev/ttyUSB0 115200,cs8

Then, I connect the other side of the cable with the display. Luckily, the touch screen starts up right away and in the screen program I can see that the display sends the following string initially:

log Geeetech LCD OK

The touch screen is usable and for some actions that I do on the touch screen, message are sent from the display. The results are listed in the following table (N-0 indicates start of a line, I guess these will normally be counted up if the control board responds):

Menu L1	Menu L2	Menu L3	Button	Command sent	Implemented
Control
Control	Home
Control	Home		Home all	N-0 G28*62	native Gcode
Control	Home		Home X	N-0 G28 X0*118	native Gcode
Control	Home		Home Y	N-0 G28 Y0*119	native Gcode
Control	Home		Home Z	N-0 G28 Z0*116	native Gcode
Control	Move
Control	Move		Enable	N-0 M17*56 N-0 G28*62	native Gcode
Control	Move		Disable	N-0 M18*55	native Gcode
Control	Move		X+ (30mm)	N-0 G91*60 N-0 G1 F6000 X30.00*48 N-0 G90*61	native Gcode
Control	Move		X- (30mm)	N-0 G91*60 N-0 G1 F6000 X-30.00*29 N-0 G90*61	native Gcode
Control	Move		Y+ (30mm)	N-0 G91*60 N-0 G1 F6000 Y30.00*49 N-0 G90*61	native Gcode
Control	Move		Y- (30mm)	N-0 G91*60 N-0 G1 F6000 Y-30.00*28 N-0 G90*61	native Gcode
Control	Move		Z+ (30mm)	N-0 G91*60 N-0 G1 F500 Z30.00*1 N-0 G90*61	native Gcode
Control	Move		Z- (30mm)	N-0 G91*60 N-0 G1 F500 Z-30.00*44 N-0 G90*61	native Gcode
Control	Move		switch to 10mm steps	N-0 L1 S1*76	not needed
Control	Move		switch to 1mm steps	N-0 L1 S2*79	not needed
Control	Move		switch to 0.5mm steps	N-0 L1 S3*78	not needed
Control	Move		switch to 0.1mm steps	N-0 L1 S4*73	not needed
Control	Move		switch to 30mm steps	N-0 L1 S0*77	not needed
Control	Motion Param
Control	Motion Param		Steps/mm	N-0 M2140 S0*122	not needed
Control	Motion Param		Velocity	N-0 M2140 S1*123	not needed
Control	Motion Param		Acceleration	N-0 M2140 S2*120	not needed
Control	Motion Param		Jerk	N-0 M2140 S3*121	not needed
Control	Motion Param		babystep	N-0 M2140 S5*127	not needed
Control	Motion Param		Double z home offset	N-0 M2140 S6*124	not needed
Control	Motion Param		Store settings	N-0 M500*11	native Gcode
Control	Motion Param	Steps/mm
Control	Motion Param	Steps/mm	X-axis up	N-0 M92 X1.00*82	native Gcode
Control	Motion Param	Steps/mm	X-axis down	nothing, maybe because no original value available	native Gcode
Control	Motion Param	Steps/mm	Y-axis up	N-0 M92 Y1.00*83	native Gcode
Control	Motion Param	Steps/mm	Y-axis down	nothing, maybe because no original value available	native Gcode
Control	Motion Param	Steps/mm	Z-axis up	N-0 M92 Z1.00*80	native Gcode
Control	Motion Param	Steps/mm	Z-axis down	nothing, maybe because no original value available	native Gcode
Control	Motion Param	Steps/mm	E0-axis up	N-0 M92 E1.00*79	native Gcode
Control	Motion Param	Steps/mm	E0-axis down	nothing, maybe because no original value available	native Gcode
Control	Motion Param	Steps/mm	Rset	N-0 M2140 R0*123	yes
Control	Motion Param	Velocity		only display
Control	Motion Param	Acceleration		only display
Control	Motion Param	Jerk		only display
Control	Motion Param	babystep
Control	Motion Param	babystep	babystep up	N-0 M290 Z0.01*96	yes
Control	Motion Param	babystep	babystep down	N-0 M290 Z-0.01*77	yes
Control	Motion Param	babystep	Rset	N-0 M290 Z0*79	yes
Control	Motion Param	Double z home offset
Control	Motion Param	Double z home offset	home-Z0 offset up	N-0 M2011 P0 S0.01*16	yes
Control	Motion Param	Double z home offset	home-Z0 offset down	N-0 M2011 P0 S-0.01*61	yes
Control	Motion Param	Double z home offset	home-Z1 offset up	N-0 M2011 P1 S0.01*17	yes
Control	Motion Param	Double z home offset	home-Z1 offset down	N-0 M2011 P1 S-0.01*60	yes
Control	Motion Param	Double z home offset	Rset	N-0 M2011 P0 S0*63 N-0 M2011 P1 S0*62	yes
Control	Leveling
Control	Leveling	manual level		N-0 M2107 S0*121	yes
Control	Leveling	manual level	Z up 0.5	N-0 M2107 S6*127	yes
Control	Leveling	manual level	Z down 0.5	N-0 M2107 S7*126	yes
Control	Leveling	manual level	Z up 0.05	N-0 M2107 S10*72	yes
Control	Leveling	manual level	Z down 0.05	N-0 M2107 S9*112	yes
Control	Leveling	manual level	Pos. 1	N-0 M2107 S1*120	yes
Control	Leveling	manual level	Pos. 2	N-0 M2107 S2*123	yes
Control	Leveling	manual level	Pos. 3	N-0 M2107 S3*122	yes
Control	Leveling	manual level	Pos. 4	N-0 M2107 S4*125	yes
Control	Leveling	manual level	Pos. 5	N-0 M2107 S5*124	yes
Control	Leveling	manual level	OK	N-0 M2107 S8*113	yes
Control	Leveling	manual level	Return	N-0 G1 F1000 Z10*25 N-0 G28*62 N-0 L101*15	yes
Control	Leveling	auto-level		N-0 M2120 P5*122	yes
Control	Leveling	auto-level	CAS	N-0 M2120 P9 S0*53	no
Control	Leveling	auto-level	3D Touch	N-0 M2120 P9 S1*52	yes
Control	Leveling	auto-level	Auto-Level on	N-0 M2120 P0 S1*61	yes
Control	Leveling	auto-level	Auto-Level off	N-0 M2120 P0 S0*60	(yes, simulated)
Control	Leveling	auto-level	Measure	N-0 M2120 P7 S0*59 N-0 M2120 P6*121	yes
Control	Leveling	auto-level	3D Touch - Push-pin up	N-0 M2120 P1 S0*61	yes
Control	Leveling	auto-level	3D Touch - Push-pin down	N-0 M2120 P1 S1*60	yes
Control	Leveling	auto-level	3D Touch - Alarm release	N-0 M2120 P1 S2*63	yes
Control	Leveling	auto-level	switch to 0.10mm	N-0 L2 S2*76	not needed
Control	Leveling	auto-level	switch to 0.05mm	N-0 L2 S3*77	not needed
Control	Leveling	auto-level	switch to 10.0mm	N-0 L2 S0*78	not needed
Control	Leveling	auto-level	switch to 1.00mm	N-0 L2 S1*79	not needed
Control	Leveling	auto-level	CAS - up	no visible effect
Control	Leveling	auto-level	CAS - down	no visible effect
Control	Leveling	auto-level	3D Touch - up 10.0mm	N-0 M2120 P3 S0*63	yes (but changed to 1.00mm)
Control	Leveling	auto-level	3D Touch - down 10.0mm	N-0 M2120 P4 S0*56	yes
Control	Leveling	auto-level	3D Touch - up 1.00mm	N-0 M2120 P3 S1*62	yes
Control	Leveling	auto-level	3D Touch - down 1.00mm	N-0 M2120 P4 S1*57	yes
Control	Leveling	auto-level	3D Touch - up 0.10mm	N-0 M2120 P3 S2*61	yes
Control	Leveling	auto-level	3D Touch - down 0.10mm	N-0 M2120 P4 S2*58	yes
Control	Leveling	auto-level	3D Touch - up 0.05mm	N-0 M2120 P3 S3*60	yes
Control	Leveling	auto-level	3D Touch - down 0.05mm	N-0 M2120 P4 S3*59	yes
Control	Leveling	auto-level	Save (value was -0.50)	N-0 M2120 P1 S2*63 N-0 M2120 P2 S-0.50*56	yes
Control	Filament
Control	Filament	Extruder 1		N-0 M165 A1.0 B0.0 C0.0*67	native Gcode
Control	Filament	Extruder 2		N-0 M165 A0.0 B1.0 C0.0*67	native Gcode
Control	Filament	Extruder 1		N-0 M165 A0.0 B0.0 C1.0*67	native Gcode
Control	Filament	Hotend on		N-0 M104 S200.0*84	native Gcode
Control	Filament	Hotend up		same as above, but with increased temp value	native Gcode
Control	Filament	Hotend down		same as above, but with decreased temp value	native Gcode
Control	Filament	Hotend off		N-0 M104 S0.0*86	native Gcode
Control	Filament	Clean on		N-0 M2105 S5*126	yes
Control	Filament	Clean off		N-0 M2105 S4*127	yes
Control	Filament	Load on (depends on selected extruder, see above)		N-0 M165 A1.0 B0.0 C0.0*67 N-0 M2105 S2*121	yes
Control	Filament	Load off		N-0 M2105 S4*127	yes
Control	Filament	Unload on (depends on selected extruder, see above)		N-0 M165 A1.0 B0.0 C0.0*67 N-0 M2105 S3*120	yes
Control	Filament	Unload off		N-0 M2105 S4*127	yes
Control	Speed
Control	Speed	Speed up (sent value = shown value)		N-0 M220 S1*76	native Gcode
Control	Speed	Speed down		no visible effect	native Gcode
Control	Speed	Fan on		N-0 M106 P0 S255*8	native Gcode
Control	Speed	Fan off		N-0 M106 P0 S0*10	native Gcode
Control	Speed	Fan up		same as on/off, but with integers representing the requested speed (selected value 0-100 mapped to sent value 0-255)	native Gcode
Control	Speed	Fan down		same as on/off, but with integers representing the requested speed (selected value 0-100 mapped to sent value 0-255)	native Gcode
Printing				N-0 M105*10 N-0 M20 LCD*87
Printing			all buttons	buttons did not have any effect
Setting
Setting	Add-on			N-0 M2139*55
Setting	Add-on		Sound on	N-0 M2139 P0 S1*53
Setting	Add-on		Sound off	N-0 M2139 P0 S0*52
Setting	Add-on		Backlight on	N-0 M2139 P1 S1*52
Setting	Add-on		Backlight off	N-0 M2139 P1 S0*53
Setting	Add-on		Backlight up (value depends on shown value 0-100)	N-0 M2139 P1 E51*23
Setting	Add-on		Backlight down (value depends on shown value 0-100)	N-0 M2139 P1 E50*22
Setting	Add-on		Screen lock on	N-0 M2139 P2 S1*55 Note: screen lock is also stored in touch unit
Setting	Add-on		Screen lock off	N-0 M2139 P2 S0*54 Note: screen lock is also stored in touch unit
Setting	Add-on		Screen lock PW (value depends on entered value, no leading zeros)	N-0 M2139 P2 W1234*6 Note: screen lock is also stored in touch unit
Setting	Add-on		Screen lock time (value depends on entered value)	N-0 M2139 P2 E16*23 Note: screen lock is also stored in touch unit
Setting	Language			no effects
Setting	ScreenCali			no effects
Setting	About			N-0 M115*11 N-0 N-0 M2134 FW:V1.02.xx*39 NOTE: 2nd and 3rd N-0 are on the same line!	yes
Setting	Factory Default
Setting	Factory Default		yes	N-0 M502*9	native Gcode
Setting	Factory Default		no	no effect (why should it?)
Setting	Detector
Setting	Detector		on	N-0 M2106 P0 S1*57	yes
Setting	Detector		off	N-0 M2106 P0 S0*56	yes
Bar chart button				N-0 M27*59
Bar chart button	Mixer Button
Bar chart button	Mixer Button		Fixed ratio mixer on	M2138 S1
Bar chart button	Mixer Button		Fixed ratio mixer on	M2138 S0
Bar chart button	Mixer Button		Change mix (see mixing ration below, example: 0%, 0%, 100%)	M2135 P6553600	yes
Bar chart button	Mixer Button		Template on	M2138 S3
Bar chart button	Mixer Button		Template off	M2138 S0
Bar chart button	Mixer Button	Template start setting	Height (height value sent)	M2137 C<value>
Bar chart button	Mixer Button	Template start setting	Color (ratio sent)	M2137 A<ratio>
Bar chart button	Mixer Button	Template end setting	Height (height value sent)	M2137 D<value>
Bar chart button	Mixer Button	Template end setting	Color (ratio sent)	M2137 B<ratio>
Main menu button				return to top menu
Return button				return to previous screen

Check 2: Listen in on communication between touch screen and control board

I use two TTL devices connected to my Linux system. One connects to the touch screen (as in the section before) and the other one connects to the control board. Hence, I have two devices: /dev/ttyUSB0 and /dev/ttyUSB1. For, it doesn't matter which device is connected to which board as I'm just listening in on the connection and I already know what the messages from the touch screen look like.

I use the tool "socat" in Linux to connect the two ports and write two files that contain the communication. The command that I use is

sudo socat /dev/ttyUSB0,b115200,raw,echo=0 SYSTEM:'tee in.txt |socat - "/dev/ttyUSB1,b115200,raw,echo=0" |tee out.txt'

This opens the first TTL, sets it to 115200 baud, outputs it to system call that writes the data into the file in.txt and forwards the input as well to the second TTL device, setting 115200 baud as well, and captures the output that device into the file out.txt. This works out great. The only thing that would be even better is to have a timestamp in the file to see what output from the control board is related to which output from the touch screen.

To do that, I try to change the output of each socket by passing it through the Linux sed tool (and some additional magic is required). Hence, my new command is

sudo socat /dev/ttyUSB0,b115200,raw,echo=0 SYSTEM:'sed -u -E \"s/^(.*)/echo \\\$(date +%T.%N) - \\1/\" | sh | tee in.txt | sed -u \"s/^.*?\-\W//\" | socat - "/dev/ttyUSB1,b115200,raw,echo=0" | tee out-orig.txt | sed -u -E -e \"s/;/#SEMICOLON#/g\" -e \"s/^(.*)/echo \\\$(date +%T.%N) - \\1/\" | sh | tee out.txt | sed -u -e \"s/#SEMICOLON#/;/g\" -e \"s/^.*?\-\W//\"'

What this does:

1. get the data from the first TTL
2. create a shell command that prepends a timestamp (e.g echo $(date +%T.%N) - <original message>)
3. execute the shell command (sh) to get the message prepended with the current time (e.g. 15:15:12.123456789 - <original message>)
4. tee the timestamped output into the file in.txt
5. remove the timestamp again so that the original message can be sent to the other TTL port
6. send the message to the other port via STDIN with socat
7. store the original data in the file out-orig.txt for later reference via tee
8. replace all semicolons in the output with the text #SEMICOLON# (as these would otherwise make trouble with the sh tool) and prepare the shell command to prepend the timestamp as above
9. execute sh to actually prepend the current timestamp
10. store the timestamped into the file out.txt
11. replace the #SEMICOLON# markers with actual semicolons again and remove the timestamp
12. data is then sent to the first TTL

The hacky solution with the sh command is required as sed does not evaluate commands in the replacement part multiple times, so always the same timestamp would be written. However, creating a script to evaluate the timestamp makes it necessary to remove/replace semicolons as they would interfere with the sh command. Anyway, the solution works and is good enough to see what is happening when.

Startup sequence

As already mentioned in the section about the touch screen commands, the first info the touch screen spits out is

log Geeetech LCD OK

This seems really to be a log message and I expect that the message is actually logged on the control board if logging is active. Nevertheless, it seems that the message is not required.

When the control board is switched on, it sends out the following messages (I removed the serial number BTW):

N-0 L3 PS:0 VL:0 MT:0 FT:0 AL:1 ST:1 WF:0 MR:100 FN: PG:0 TM:0 LA:0 LC:0*5
N-0 L1 X0.000 Y0.000 Z0.000 F0*13
N-0 L2 B:0.0 /0.0 /0 T0:0.0 /0.0 /0 T1:0.0 /0.0 /0 T2:0.0 /0.0 /0 SD:1 F0:0 F2:50 R:100 FR:0*100
N-0 L3 PS:0 VL:0 MT:0 FT:0 AL:1 ST:1 WF:0 MR:100 FN: PG:0 TM:0 LA:0 LC:0*5
N-0 L9 DN:GEEETECH-A30T;DM:A30T;SN:<removed>;FV:V1.xx.03;PV:320.00 x 320.00 x 420.00;HV:V1.6;*6
N-0 L22 MS:0 MR:100 SP:100 EP:100 SH:0.00 EH:0.00*63
N-0 L24 P3 A7.00 B7.00 C0.50 D5.00*126
N-0 L24 P3 A7.00 B7.00 C0.50 D5.00*126
N-0 L24 P3 A7.00 B7.00 C0.50 D5.00*126
N-0 L24 P3 A7.00 B7.00 C0.50 D5.00*126
N-0 L23 SE:0 BE:1 BP:50 CE:0 HE:0 SP:0 ST:16 HC:0 HO:0*23
N-0 L23 SE:0 BE:1 BP:50 CE:0 HE:0 SP:0 ST:16 HC:0 HO:0*23
N-0 L2 B:27.2 /0.0 /0 T0:30.7 /0.0 /0 T1:89.6 /0.0 /0 T2:107.3 /0.0 /0 SD:1 F0:0 F2:50 R:100 FR:0*85
N-0 L18 P26 S1*0
N-0 L21 P0 S0*63
N-0 L3 PS:0 VL:0 MT:0 FT:0 AL:1 ST:1 WF:0 MR:100 FN: PG:0 TM:0 LA:0 LC:0*5
N-0 L21 P0 S0*63
N-0 L21 P0 S0*63
N-0 L3 PS:0 VL:0 MT:0 FT:0 AL:1 ST:1 WF:0 MR:100 FN: PG:0 TM:0 LA:0 LC:0*5
N-0 L21 P0 S0*63
N-0 L21 P0 S0*63
N-0 L2 B:27.3 /0.0 /0 T0:29.0 /0.0 /0 T1:89.4 /0.0 /0 T2:107.4 /0.0 /0 SD:1 F0:0 F2:50 R:100 FR:0*94
N-0 L3 PS:0 VL:0 MT:0 FT:0 AL:1 ST:1 WF:0 MR:100 FN: PG:0 TM:0 LA:0 LC:0*5
N-0 L21 P0 S0*63
[...]

The L21 P0 S0 command is repeated until the touch screen answers with its firmware version. L1, L2 and L3 seem to be status messages that are sent either regularly (L3) or only when something changes. I'll now try to find out what the specific parameters of the messages mean. My findings about the codes and their parameters can be seen in the following two tables.

Basic data exchange format description

I created this section and also extended the following ones based on the info provided in this issue comment. I took the PDF and translated it to english with Google translate.

Letter	Definition
Lnnn	Commands received by the touch screen
Pnnn	Command parameters (e.g. file list file name)
Tnnn	Command parameters, most likely only tool selection
Snnn	Command parameters (e.g. temperature value)
Xnnn	X axis coordinate in mm
Ynnn	Y axis coordinate in mm
Znnn	Z axis coordinate in mm
Fnnn	Feedrate in mm/s
Ennn	Length of extruded material in mm (I've never ever seen this anywhere being used)

Each command sent/received by the control unit or the display is prefixed with the line numer N-0, suffixed with a checksum *nnn and terminated with \r\n. The touch screen receives only L nessages, but sends out G, L and M messages. The G ones are mostly standard, L codes are all proprietary and M messages are mixed. In the latter case, the 3-digit codes seem standard and the proprietary ones seem to use 4-digit codes (look also here)

Sent from control board

Examples can be found here. According to the section above, the display only receives L commands.

Code	Field	Meaning	Answer	Implemented
L1		sent to transmit position of X, Y and Z as well as feedrate		yes
L1	X	X position in mm
L1	Y	Y position in mm
L1	Z	Z position in mm
L1	F	Feedrate in mm/s
L2		sent to transmit status of temperatures etc. (only on changes)		yes
L2	B	Bed temperature (current / target / on/off)
L2	T0	Extruder 0 temperature (current / target / on/off)
L2	T1	Extruder 1 temperature (current / target /on/off) (shows strange values, machine has only one extruder)
L2	T2	Extruder 2 temperature (current / target /on/off) (shows strange values, machine has only one extruder)
L2	SD	0 = SD card present, 1 = no SD card present, 2 = SD card failed (according to documentation also covers U-disk, but no idea what that is (USB disk?) and I don't need it)
L2	F0	Cooling fan speed (values 0 - 100)
L2	F2	Motherboard fan speed (from my research the fan runs at fixed speed and the only value ever provided is 50)
L2	R	Printin speed (values 10 - 800)
L2	FR	Feedrate in mm/s
L3		transmit print status		yes
L3	PS	print status: 0 = idle, 1 = printing, 2 = paused, 3 = recovery, 4 = finished
L3	VL	0 = printed from SD, 1 = printed from U-disk
L3	MT	motor tension: 0 = disabled, 1 = enabled
L3	FT	filament sensor: 0 = on (one sensor has no filament), 1 = on (all sensors detected filament), 255 = off
L3	AL	auto leveling: 0 = off, 1 = on
L3	ST	Bed leveling sensor type: 0 = capacitive proximity switch, 1 = BLtouch
L3	WF	Wifi exists: 0 = no, 1 = yes
L3	MR	Mix ratio: a number between 100 (E0 active), 25600 (E1 active) and 6553600 (E2 active). Calculation: lower 8 bits = percent of E0, next 8 bits = percentage E1, upper 8 bits = percentage E2 (all decimal numbers; summing up to 100)
L3	FN	file name
L3	PG	print progress (0-100 in %)
L3	TM	seconds since start of print
L3	LA	active layer of current print
L3	LC	layer count of current file
L4		Wifi status (will not implement as I don't have the adapter)		no
L5		Printing rate (will not implement, haven't seen this, yet)		no
L6		Fan status (will not implement, haven't seen this, yet)		no
L7		SD file list with multiple lines
L7	begin file list:n	start of the file list: 0 = SD card
L7	P	0-indexed file list of the selected folder
L7	end file list:n	end of the file list: 0 = SD card
L8		Upload file to screen (will not implement, haven't seen this, yet)		no
L9		sends information about the control board, shown in "about" screen. Parameters are semicolon-separated, not space separated		yes
L9	DN	Device name
L9	DM	Device model
L9	SN	Serial number
L9	FV	Firmware version
L9	PV	Print volume
L9	HV	Hardware version
L10		Manual leveling result (can have more parameters as per documentation, but I've never seen that)		yes
L10	S	Z value
L11		Automatic leveling saved result		yes
L11	P	Always 0
L11	S	Z offset
L12		??? P0 S0?		no
L13		Disk selection (never seen, will not be implemented)
L14		Send message to printing progress display		yes
L15		Filament sensor switch result (not used, but L3 is used instead)		no
L16		Power-off resume functionality (will not implement)		no
L17		Reserved for motor movement result (not used)		no
L18		Error messages		yes
L18	P	Interface version (only seen version 26 seen so far)
L18	S	Error code: 0 = no filament, 1 = SD card removed, 2 = resume print?, 3 = file not found, 4 = hotend temperature abnormal, 5 = bed temperature abnormal, 6 & 7 = bed temperature abnormal, print job stopped, 8 & 9 = bed temperature abnormal, user should kill job, 10 = could not open file, 11 = 3Dtouch alarm (check and retry), 12 = hotend too cold to change filament, 13 = operation unavailable during print, 14 = terminate PID Autotune? (yes -> send M108 and M27 to board), 15 = wait for user to continue (ok -> send M0 to board) >=16 = empty message box with yes and no option
L19		Status for stepper control (will not implement)		no
L20		Update firmware (will not implement as not used)		no
L21		request display firmware version with P0 S0	M2134	yes
L22		Status of mixing templates
L22	MS	???
L22	MR	Mix ratio, see L3 MR
L22	SP	Start percentage
L22	EP	End percentage
L22	SH	Start height
L22	EH	End height
L23		add-on status		no
L23	SE	sound enabled: 0 = off, 1 = on
L23	BE	backlight setting enabled: 0 = off, 1 = on
L23	BP	backlight percent: value 1 - 100
L23	CE	code enabled: 0 = disabled, 1 = enabled
L23	HE	Heater enabled (not used)
L23	SP	set password: 4 digit value (no leading zeros)
L23	ST	screen lock time: number in seconds (at least two digits)
L23	HC	Heater center deviation (not used)
L23	HO	Heater temperature offset (not used)
L24		info about settings		yes
L24	P0	steps/mm: A = X axis, B = Y axis, C = Z axis, D = extruder E0
L24	P1	velocities (mm/s): A = X-VMax, B = Y-VMax, C = Z-VMax, D = E-VMax, E = VMin, F = VTravel
L24	P2	accelerations (steps/s2): A = Accel, B = A-Retract, C = X-Max accel, D = Y-Max accel, E = Z-Max accel, F = E-Max accel
L24	P3	jerks (mm/s): A = Vx-jerk, B = Vy-jerk, C = Vz-jerk, D = Ve-jerk
L24	P5	babystep (mm): A = value
L24	P6	double-z home offset: A = home-Z0 offset, B= home-Z1 offset

Sent from touch screen (non standard G-Code as per this)

Examples can be found here.

Some definitions can also be found in the Geeetech Github project, however, not all of them are accurate (see e.g. filament sensor on/off).

Code	Field	Meaning	Expected answer
L1		set stepping for manual move
L1	S	0 = 30mm, 1 = 10mm, 2 = 1mm, 3 = 0.5mm, 4 = 0.1mm
L2		set stepping for auto leveling
L2	S	0 = 10mm, 1 = 1mm, 2 = 0.1mm, 3 = 0.05mm
L101		??? finished manual leveling?
M20		Get SD file list (requires a specific answer)	L7
M27, M2101		Request print status (requires a specific answer)	L3
M104, M105, M140		Get/set temperatures (requires a specific answer)	L2
M106		Set fan speed (requires a specific answer)	L6
M114, G1, G28		Get/set positions (requires a specific answer)	L1
M115		Get firmware info (requires a specific answer)	L9
M220		Set print rate (requires a specific answer)	L5
M2011		control double z home offset
M2011	P	0 = Z0, 1 = Z1
M2011	S	offset value
M2100		Trigger LCD firmware upgrade (will not implement)
M2103		*??? something like "start/stop print"?
M2105		filament stuff
M2105	S	2 = load, 3 = unload, 4 = all motors off, 5 = cleaning on (cycle motors)
M2106		filament sensor
M2106	P0	S0 = off, S1 = on
M2107		manual leveling
M2107	S0	home and start	L10, M2107 Z:%3.2f
M2107	S1	go to pos 1 (RR)	L10, M2107 ok or M2107 fail
M2107	S2	go to pos 2 (RL)	L10, M2107 ok or M2107 fail
M2107	S3	go to pos 3 (FL)	L10, M2107 ok or M2107 fail
M2107	S4	go to pos 4 (FR)	L10, M2107 ok or M2107 fail
M2107	S5	go to pos 5 (C)	L10, M2107 ok or M2107 fail
M2107	S6	Z up 0.5mm	L10, M2107 Z:%3.2f
M2107	S7	Z down 0.5mm	L10, M2107 Z:%3.2f
M2107	S8	save	L10, M2107 save success
M2107	S9	Z up 0.05mm	L10, M2107 Z:%3.2f
M2107	S10	Z down 0.05mm	L10, M2107 Z:%3.2f
M2107	S11	exit	L10
M2111		Motor movement (never seen, will not implement)
M2111		Disk selection instruction (is this required for SD printing?)
M2120		auto leveling
M2120	P0	auto level on/off: S0 = off, S1 = on	L11
M2120	P1	3D Touch pin control: S0 = pin up, S1 = pin down, S2 = alarm release
M2120	P2	store offset value: S = value	L11
M2120	P3	offset up: S0 = 10mm, S1 = 1mm , S2 = 0.1mm, S3 = 0.05mm	L1
M2120	P4	offset down: S0 = 10mm, S1 = 1mm , S2 = 0.1mm, S3 = 0.05mm	L1
M2120	P5	request Z offset	L11
M2120	P6	move nozzle to center	L1
M2120	P7	S0 = move probe to center and measure	L1
M2120	P9	select probing device: S0 = CAS, S1 = 3D Touch
M2130		Power-off resume control (will not implement)
M2131		Configure Wifi (will not implement)
M2132		Adjusting stepper control (will not implement)
M2133		Abnormal situation (not seen yet, will not implement)
M2134		send firmware version
M2134	FW:	the firmware version
M2135		set current mixing rate	L22
M2135	P	Mixing rate bitfield as decimal (see MR above)
M2136		define mixing template (not seen yet, will not be implemented)	L22
M2137		set current mixing template (I've never used this, will most likely not implement)	L22
M2137	A	Mixing ratio start (see MR above)
M2137	B	Mixing ratio end (see MR above)
M2137	C	Mixing start layer number
M2137	D	Mixing end layer number
M2138		Set mixing mode	L22
M2138	S	0 = off, 1 = fixed, 3 = template
M2139		add-on stuff
M2139	P0	sound settings: S0 = off, S1 = on
M2139	P1	backlight settings: S0 = off, S1 = on, E<value 0-100> = set brigthness
M2139	P2	screen lock: S0 = off, S1 = on, W<4 digits> = set password, E<2 digits> = set lock time
M2139	P3	Extruder temperature deiation (not used)
M2140		control settings
M2140	S	0 = steps/mm, 1 = velocity, 2 = acceleration, 3 = jerk, 4 = ???, 5 = babysteps, 6 = double z home offset
T0, T1, T2		Set tool (requires a specific answer)	L22

Check 3: Send some commands directly to the touchscreen

To get this to work I had to play around a little bit with different commands as I could not figure out at first why I couldn't communicate with the touchscreen. Nevertheless, after some fiddeling around I found a way to send commands. I use the command minicom to send commands, however, I currently cannot just type them in but I have to type the commands including the newline in a text editor and copy them into minicom. I guess my CR/LF stuff is currently not working as expected. Nevertheless, copying and pasting the commands worked. One of the things I identified is that I have to send the command including the N-0 part at the start and I have to add the *<number here> part as well. Hence, I think I have to figure out what the number at the end is. I guess it's just a simple checksum that has to be calculated as it is always the same if the command does not change. I'll look at my examples and try to figure out what the numbers mean.

What I've found so far is that the number after the * never goes beyond 127, but it seems any number including 0 can show up there. I've extracted the following commands from my examples to have a basis for further analysis:

N-0 L24 P5 A0.03*0
N-0 L24 P5 A0.12*0
N-0 L24 P5 A0.21*0
N-0 L24 P5 A0.30*0

N-0 L24 P5 A0.02*1
N-0 L24 P5 A0.13*1
N-0 L24 P5 A0.20*1

N-0 L24 P5 A0.01*2
N-0 L24 P5 A0.10*2
N-0 L24 P5 A0.23*2

N-0 L24 P5 A0.00*3
N-0 L24 P5 A0.11*3
N-0 L24 P5 A0.22*3

N-0 L24 P5 A0.07*4
N-0 L24 P5 A0.16*4

N-0 L24 P5 A0.06*5
N-0 L24 P5 A0.17*5
N-0 L24 P5 A0.24*5

N-0 L24 P5 A0.05*6
N-0 L24 P5 A0.14*6

N-0 L24 P5 A0.04*7
N-0 L24 P5 A0.15*7

N-0 L24 P5 A0.09*10
N-0 L24 P5 A0.18*10

N-0 L24 P5 A0.08*11
N-0 L24 P5 A0.19*11

N-0 M2120 P9 S1*52
N-0 M2120 P9 S0*53
N-0 M2120 P7 S0*59
N-0 M2120 P0 S0*60
N-0 M2120 P1 S1*60
N-0 M2120 P0 S1*61
N-0 M2120 P1 S0*61

N-0 M2120 P1 S2*63

N-0 M2107 S10*72

N-0 M2107 S9*112
N-0 M2107 S8*113

N-0 M2107 S1*120
N-0 M2107 S0*121
N-0 M2120 P6*121
N-0 M2107 S3*122
N-0 M2120 P5*122
N-0 M2107 S2*123
N-0 M2107 S4*125
N-0 M2107 S7*126
N-0 M2107 S6*127

I ordered the first few sorting by command:

N-0 L24 P5 A0.00*3
N-0 L24 P5 A0.01*2
N-0 L24 P5 A0.02*1
N-0 L24 P5 A0.03*0
N-0 L24 P5 A0.04*7
N-0 L24 P5 A0.05*6
N-0 L24 P5 A0.06*5
N-0 L24 P5 A0.07*4
N-0 L24 P5 A0.08*11
N-0 L24 P5 A0.09*10
N-0 L24 P5 A0.10*2
N-0 L24 P5 A0.11*3
N-0 L24 P5 A0.12*0
N-0 L24 P5 A0.13*1
N-0 L24 P5 A0.14*6
N-0 L24 P5 A0.15*7
N-0 L24 P5 A0.16*4
N-0 L24 P5 A0.17*5
N-0 L24 P5 A0.18*10
N-0 L24 P5 A0.19*11
N-0 L24 P5 A0.20*1
N-0 L24 P5 A0.21*0
N-0 L24 P5 A0.22*3
N-0 L24 P5 A0.23*2
N-0 L24 P5 A0.24*5
N-0 L24 P5 A0.25*4
N-0 L24 P5 A0.26*7
N-0 L24 P5 A0.27*6
N-0 L24 P5 A0.28*9
N-0 L24 P5 A0.29*8
N-0 L24 P5 A0.30*0
N-0 L24 P5 A0.31*1
N-0 L24 P5 A0.32*2
N-0 L24 P5 A0.33*3
N-0 L24 P5 A0.34*4
N-0 L24 P5 A0.35*5
N-0 L24 P5 A0.36*6
N-0 L24 P5 A0.37*7
N-0 L24 P5 A0.38*8
N-0 L24 P5 A0.39*9
N-0 L24 P5 A0.40*7

I also looked for the shortest entries I could find:

N-0 G28*62
N-0 M27*59

Points that seems interesting:

• since all numbers are lower than 128, maybe there is a modulo by 128 in there?
• I can see from the sorted commands that although single character codes (in ascii) are increasing, the number at the end can increase or decrease independently
• although the commands in the sorted list keep changing, their number does not go beyond 11

Maybe one idea for further investigation: Send M117 commands to the printer via the USB port and see how these are passed on to the display?

After some googling I found this information in the Reprap wiki. It seems, for g-code the characters are just combined using XOR. That could explain the strange behavior. I'll have to figure out the encoding now, try to calculate the checksum based on that and compare it with what I've seen in the examples.

I've tested the described algorithm with the default ascii encoding and using XOR on that: Original line: N-0 G28*62 G-code to build checksum for: N-0 G28

Decimal ascii values of the characters:

N = 78
- = 45
0 = 48
  = 32 (space)
G = 71
2 = 50
8 = 56

I put these decimal numbers into this nice online XOR calculator and, tadaa, the decimal result ist 62 (as what was sent from the control board). The same worked out for the N-0 M27*59 command. I haven't checked the others, but I'd expect them to work as well. Hence, to send some commands to the display manually I have to send the commands including the checksum. Now I also think I can understand why Geeetech prefixed all their lines with N-0 . The Reprap wiki entry linked above states that if you want checksums you need line numbers. I guess Geeetech wanted to have checksums to ensure correct transmission of commands but didn't want to keep track of line numbers.