Modbus CNC Spindle Control (3.6 RC2) Shihlin SL3

Firky_CNC

Very interested in the use of MODBUS on the Duet platform. While the duet mini 5 + doesn't support Modbus directly, using a UART on Aux 1 to a TTL to RS485 Adapter Module 3.3V ( Youmile). However, I'm not able to control the VFD from the Duet.

I have found only one thread that discusses the options of using a converter. Here's where I am so far:

In config.g

M575 P2 B9600 S7 ; Enable IO_1 for MODBUS RTU at 9600 baud, 8E1

Wiring :

Duet Pins-------------->Youmile Pins
Pin 1 (3.3V)--------------> VCC
Pin 3 (GND)-------------> GND
Pin 4 (IO_1_out = TX) ---> RXD
Pin 2 (IO_1_in = RX) -----> TXD

SL3 configuration
07-00 Communication control enable 0 Enables MODBUS
07-01 Station number (device ID) 1 Match Duet G-code A1
07-02 Baud rate 1 9600 bps
07-07 Format 4 RTU mode (1,8,E,1)

The TX light on the converter flashes when sending M261.1 P2 A1 F3 R0 B1 V"reg0"; however returns Error: M261.1: no or bad response from Modbus device.

The RX light on the converter only flashed when the VFD is first started.

See below my Config.g file. This is just a test situation with one axis somewhat configured.

; Configuration file for Duet 3 Mini 5+ (firmware version 3.6.0-rc.2+2)
; Config Version: 1.1 - Updated 2025-04-14
; • Fixed invalid string concatenation for error messages
; • Added full MODBUS spindle control and safety interlock

; General preferences
; M952 B121 A51 ; change the CAN address of expansion board 121 to 51
G90 ; send absolute coordinates
M83 ; ...but relative extruder moves
M550 P"Tiny_Mill" ; set printer name
M453 ; select CNC device mode

; Drives
M569 P0.0 S1 ; physical drive 0.0 goes forwards
M569 P51 S1 D4 ; physical drive 121.0 goes forwards
M569.1 P51 T2 C5 E0.1:2.0 H0.8 ; Stepper driver closed loop configuration
M569 P0.2 S1 ; physical drive 0.2 goes forwards
M569 P0.3 S1 ; physical drive 0.3 goes forwards
M584 X0.0 Y51 Z0.2 E0.3 ; set drive mapping
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z400.00 E420.00 ; set steps per mm
M566 X900.00 Y900.00 Z60.00 E120.00 ; set max instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z180.00 E1200.00 ; set max speeds (mm/min)
M201 X500.00 Y500.00 Z20.00 E250.00 ; set accelerations (mm/s^2)
M906 X800 Y2000 Z800 E800 I30 ; set motor currents (mA) and idle factor in %
M84 S30 ; Set idle timeout

; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X230 Y210 Z200 S0 ; set axis maxima

; Endstops
M574 Y1 S1 P"51.io0. in" ; endstop for low end on Y

; Z-Probe
M558 P0 H5 F120 T6000 ; disable Z probe, set dive height/speeds
M557 X15:215 Y15:195 S20 ; define mesh grid

; Heaters
M140 H-1 ; disable heated bed

; Tools
M563 P0 D0 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; tool 0 axis offsets
G10 P0 R0 S0 ; tool 0 standby and active temps

; RS485 MODBUS for SL3 VFD (via M260.1 and M261.1)

M950 P0 T2 ; Define logical spindle 0 for object model access (spindles[0])
M575 P2 B9600 S7 ; Enable IO_1 for MODBUS RTU at 9600 baud, 8E1

; Example MODBUS write commands using M260.1:
; Start forward (write 0x0002 to H1001 = register 4097)
; M260.1 P2 A1 R4097 B2
; Start reverse (write 0x0004 to H1001)
; M260.1 P2 A1 R4097 B4
; Stop (write 0x0000 to H1001)
; M260.1 P2 A1 R4097 B0
; Emergency stop (write 0x007F to H1001)
; M260.1 P2 A1 R4097 B127
; Set frequency: write value (e.g. 30000 = 300.00 Hz) to H1002
; M260.1 P2 A1 R4098 B30000

; Optional Read Monitoring (manual trigger or used in macros)
; Read spindle state (5 registers starting at H1001)
M261.1 P2 A1 F3 R4097 B5 V"spindleState"
; Read output frequency (H1003)
M261.1 P2 A1 F3 R4099 B1 V"spindleFreq"
; Read output power (H101B)
M261.1 P2 A1 F3 R4123 B1 V"spindlePower"
; Read fault/error codes (H1003-H1004)
M261.1 P2 A1 F3 R4103 B2 V"spindleErrors"

; Safety Interlocks & Error Handling
if { exists(global.spindleErrors) && global.spindleErrors != null && global.spindleErrors[0] != 0 }
M118 S"[MODBUS] VFD error detected." L1
M118 S{"VFD error code = " ^ global.spindleErrors[0]} L1
abort "VFD Error - Operation halted."

; These values can be accessed in object model via global variables after being read.

jay_s_uk

@Firky_CNC I control an SL3 is RRF on my Milo Mill.
One of the Milo Guys (@NineMile) has been developing the SL3 control stuff so it may be easier for you to test his stuff out.
Discord is probably the best place to go https://discord.gg/Bn55Hj2Tsj

Firky_CNC

@jay_s_uk Thanks, I've joined the discord, need to be a member 10 mins before I can post while I wait. Are you able to confirm if you have a specific mode that you need to put the VFD in to receive Modbus commands?

jay_s_uk

@Firky_CNC i'm at work so I can't remember off the top of my head what registers need changing on the VFD