Support for RS485 on Duet 6XD and 6HC

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

Screenshot 2024-08-13 151345.png

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

dc42

@developeralgo222 RRF doesn't yet support writing coils or reading discrete inputs, I only implemented writing registers, reading input registers, and reading holding registers.

Your document gives register numbers in hex. RRF takes parameters in decimal by default, but you can use hex numbers like this:

M260.1 P1 A1 R{0x0029}  B1

developeralgo222

@dc42 Fantastic.

When do you think you will be able to get to implementing the coils part , The SMT feeders i am testing it on needs to be able to Read/Write Coils to turn the Feeder triggers ON or OFF ?

dc42

@developeralgo222 I've attempted to add Modbus coil support but I don't have a Modbus device that implements coils to test it on. I've put a new MB6XD binary at https://www.dropbox.com/scl/fo/gwhkwjg232hd6us8yvr0k/ABiZ84dcbZEb9PYiznBRMZU?rlkey=whab6c638wj8w4hyo2jyvjign&dl=0.

developeralgo222

@dc42 i will try and test the coils with the new binary now

dc42

@developeralgo222 M260.1 now takes a F parameter to specify the Modbus function number. See https://docs.duet3d.com/en/User_manual/Reference/Gcodes#m2601-modbus-write-registers-or-coils.