Support for RS485 on Duet 6XD and 6HC

[developeralgo222]

@dc42 is there any Alternative while i wait for a stable solution. I have 60+ Electric feeders that i need working in 4 days for a client production job ? Any suggestions on a RS485 converter to get if required and the wiring connections that for the time being can accomplish this

My Older discussion is here : https://forum.duet3d.com/topic/35524/does-duet-6xd-support-rs485-communication/5?_=1719243430041

Since there is no specific timeline for RS485 Support in RRF at the moment

[developeralgo222]

@dc42
Currently with existing boards Would such a TTL (UART) to RS485 Converter Compatible with 3.3V and 5.0V signals work plus Spare IO (IO0 or IO1 ) port on Duet 6XD ?

Below is Option 2: Using already existing RRF 3.5.2 CAN support by utilizing CAN0 AUX Port i.e Duet 6XD CAN0 AUX Port <==> CAN-RS485 MODBUS Converter <==> FX3U-485ADP-MB

Below are the links to the adapters or converters for the 2 options:

CAN-to-RS485 Converter:
https://www.amazon.ca/dp/B0CSFH8QTN/?coliid=I35EGBMWD8HST8&colid=2QAEOOXW12HBB&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it

UART(TTL) To RS485 (B) Converter
https://www.amazon.ca/gp/product/B0BQFB7JCK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

[dc42]

@developeralgo222 yes that board looks good, although it's more complicated than RS485 boards that I have used before.

[developeralgo222]

@dc42 As for communications commands from Duet 6XD to the electric feeder using the above setup ( RS485 Converter + IO0 Port ) . Can you please elaborate using RRF 3.5.2 commands with an example of a simple communication ?

[developeralgo222]

@dc42, @T3P3Tony ,@droftarts Also what is the Maximum UART Port Speed that IO0 or IO1 can handle on Duet 6XD since i think default UART clock is 3MHz but Apparently UART CLOCK can go as high as 100MHZ. The maximum baud rate is clock/16.

So what is the Maximum Speed of UART Port on Duet 6XD without corruption of data ? 115200 bps ?

[dc42]

@developeralgo222 maximum transmission speed is much higher than that. However, it you try to receive data above about 57600 baud then you may suffer character loss because of interrupt latency.

[developeralgo222]

@dc42 so what would be the recommended fastest baud rate to use with Duet 6XD?

[developeralgo222]

@developeralgo222 also is it possible for one of your devs to add the support for RS485 MODBUS RTU to the unofficial dev version of RRF 3.5.2+ or 3.6 dev and I will act as tester for it because I really have an urgent huge need for RS485 MODBUS RTU for Duet 6XD or if one of your devs can provide the code , I can try and compile a dev version to use while waiting for the support to be included in official “After” RRF 3.6 version. I am really desperate to get this done , I need to control and communicate to over 60+ Electric SMT feeders using RS485 MODBUS RTU. This is really , really urgent , time is not on my side

[dc42]

@developeralgo222 I have just returned from holiday. My immediate priority this week is to fix bugs in 3.6 that our alpha testers have reported. When that's done I may get time to implement Modbus support in 3.6.

[developeralgo222]

@dc42 , Thanks , i hope you got well needed rest on your vacation and you can get time to work on this. I understand the priority but our very Large project is now at a standstill, We are a large project completely based on Duet 6XD & 3HC products with our Total cost into Tens of thousands of $$$$$. we can't get it working without RS485 MODBUS RTU communications from Duet 6XD being supported. I am willing at moment to be one of the Alpha testers for 3.6.x with this RS485 MODBUS RU enabled.

[dc42]

@developeralgo222 I've put a preliminary build of RRF 3.6.0 for the 6XD with experimental Modbus RTU support at https://www.dropbox.com/scl/fo/868isq8kjcmgy1k7z7b3g/ADwxJUoidmE1XRYFZWMdCWk?rlkey=w8imtto9wirwitm5ac2xamxap&dl=0. I've only tested reading input registers, and only from one Modbus device. However as I won't be able to work on this again until next week, I'm making it available in case it is of any use to you.

To use Modbus:

• Connect a UART to RS485 converter to IO0 or IO1 of the 6XD
• Use the new S7 parameter and optionally the new C parameter of the M575 command to set the chosen port to Modbus mode, set the baud rate, and set the port to drive the Tx/!Rx input of the RS485 transceiver if required (that can be any other io#.out port)
• Use the new M260.1 command to write Modbus registers and/or the new M261.1 command to read Modbus input registers. Note, the M261.1 command V parameter is not implemented yet.

[gloomyandy]

@dc42 Do you have a recommendation for a suitable converter? Most of the ones on Amazon seem to use automatic switching. This one seems to have enable pins: https://www.amazon.co.uk/WINGONEER-MAX485-Module-RS-485-Development/dp/B06XHHWLMW

[developeralgo222]

@dc42 i will continue testing

[dc42]

@developeralgo222 latest binaries are at https://www.dropbox.com/scl/fo/yc7mnauicu5vqw6yegeq7/AKnV4j8k1MCADG4VE4EIG6Y?rlkey=skjxh23i9c953yvxm2tb8qr36&dl=0.

[developeralgo222]

@dc42

i am testing with the following GCODE. Can you review to see if i am doing it correctly

M575 P1 B115200 S7  ; Set Serial comms parameters TX & RX
M260.1 P1 A1 R42 B1 ; Modbus Write to registers / Coils 
M261.1 P1 A1 R42 B2 ; Modbus Read from Holding or Input registers / Coils 

Below is:

RS485 Serial Connections Configurations on the PLC MODBUS RTU Side:

Modbus Slave Address (PLC):  1 

Comm Mode :   RS485  Modbus RTU 

Parameters:   115200, 8Bit, None, 1Bit

i.e 

Baudrate : 115200
Length: 8 
Parity : None
Stop Bits: 1

Hardware Control:
Flow Control Mode: No 
DTR: Enable
RTS: Enable

[dc42]

@developeralgo222 you only need one M575 P1 command, and the C parameter should only be used if your RS485 adapter has a Tx/Rx control input.

The V parameter of M261.1 is not yet implemented.

[developeralgo222]

@dc42 as edited above ?

[dc42]

@developeralgo222 yes, if your RS485 adapter does automatic Tx/Rx switching, and you want to write 1 word with value 1 to register 42 and then read registers 42 and 43.

It might be a good idea to try with a lower baud fate initially e.g. 19200. The automatic Tx/Rx switching will probably only work over a range of baud rates. 9600 and 19200 are commonly used for Modbus RTU.

[developeralgo222]

@dc42 , i managed to have it working at 115200. Need to go through simple tests

As per your statement above so far Function Code:

0x03 (Read Holding registers ) and 0x04 (Read input registers ) are working and i can also write to a single Register but i can't seem to be able force a single coil to ON (1) or OFF (0) directly

[developeralgo222]

@developeralgo222 FX3U MODBUS Serial Communication Edition.pdf

If you review pages 55 - 75 & 95 on the PDF that has Modbus Format & address mapping for the device i have FX3U

. I am trying to Write a single Coil to turn it ON(1) of OFF (0)

; Write to a single coil  Mxxx   e.g M41 (which has address 0x0029)  in order to turn it ON(1) = FF00  or OFF(0) = 0000

M260.1 P1 A1 R0x0029  B1

; Read a  single coil M41 (which has address 0x0029)  in order to turn it ON(1) = FF00  or OFF(0) = 0000

M260.1 P1 A1 R0x0029  B1

i don't seem to be able to format it correctly with Duet 6XD, any help on the formatting. i don't get errors but seem to be writing to correct Register

---

M260.1: Modbus write registers
Supported from firmware version 3.6

Write data to a Modbus slave device.

Parameters

• Pnn -- Serial port to send/receive through, numbered as in M575 (1 = first aux port, 2 = second aux port). The port must already have been set to Modbus mode using M575.
• Ann -- Modbus slave device address
• Rnn -- First Modbus register number to send data to
• Bnn:nn:nn... --- 16-bit words to send

---

is the register number Rnn in Hexadecimal or decimal ? i presume it should be in Hex format ? what is the correct format , can you give an example using Coil M41 in my case . Note: i am able to turn it ON or OFF using Modbus RTU connection from my laptop or manually on the FX3U config app

Here is some snapshot captures (Request & Response ) of the MODBUS communications between MODBUS Master (Open Modscan on a PC ) and Slave ( Mitsubishi FX3U-48MR PLC with FX3U-485ADP-MB Adapter) when testing various functions:

Jabit_FX3U_Modbus_Comms_Capture.pdf