Rail-mount SX1262 LoRa Data Transfer unit (Outputs RS232/RS485/RS422) (CE09352)

Support Product Questions
41

Do the 3 have a common ground ?

In theory RS485 should be differential and not really need one, but then again what is the reference voltage ?

Is it possible to test with a ground wire ?

Also, for reference, your unit should only be LF or HF not both.
In AU it should be HF and start at 915-930.
but the unit will be 850~930Mhz for channel #0-80

42

Hi Aan
You have got both ends of the RS485 lines terminated with 120Ω haven’t you. If not you will get echos off the open ends of the line which will corrupt the data.
If you are using some sort of adaptors these terminating resistors might already be there. To check disconnect the A and B wires and measure the resistance across the adaptor connection. If you measure about 120Ω you are ok, if not you will have to fit the resistors across A and B wires.
Cheers Bob
Edit 04/01: added the word “adaptor” between “the” and “connection” above

43

To add to Bob’s post
The SX1262 Unit has two jumpers for the 120 ohm terminations. On my units both defaulted to “on” i.e. the 120 ohm resister was part of the circuit.

From my image, the left one is the 2nd for the RS422, while the right one is used for RS422 and RS485.

So It could be worth playing with that. If your other 2 devices are at each end of the bus and you are adding one of these units to “sniff” the traffic, you may be adding a 3rd termination resistor.

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44

Hi All
In all of the RS485 systems I have dealt with the criteria are as follows
The drivers are designed to operate into a MAX load of 56Ω (I think this is the figure) which would comprise:
Two 120Ω resistors, one at each END of the transmission line (60Ω), plus 32 UNTERMINATED drops connected in parallel along that line.
The transmission line MUST be terminated at the receiving end. In this case being half duplex both ends receive so both ends are terminated. NO terminations in between.
If the system is SIMPLEX (one way) the termination is required at the receiving end only.

I think this is some sort of spec for RS485 as in Maxim data sheet.

It has been a very long time since I had any practical involvement but most of the devices I dealt with were purpose built and had 2 terminals, Data line in and Data line out. The “out” terminal was a convenient place for the terminating resistor at the “end of the line” device.
Cheers Bob

45

Thanks for the replies.
I have tried a lot of the suggestions and have narrowed it down to a PLC issue.
I can now connect two rs485 dongles to the computer and transmit flawlessly over lora. The HMI also transmits flawlessly.

The issue is possibly an incompatability with the way the PLC replies to queries.
If i transmit “:010208000010E5” from the computer it responds correctly with “:0102020000FB” about 5-20% of the time depending on baud rate. The other times the response is garbled.

46

Im assuming that all devices have the same baud rate set (as well as all other settings… i.e. data bits, parity, stop bits, flow control. Maybe its uart clock is a little out?
Im sure you checked it all, but may be worth double check.

47

Yeah, I have checked it all.
Also the HMI and PLC communicate fine over wire, then the HMI transmits fine over lora to the PC,this should indicate all divices have the same settings.

48

It would be interesting to data collect the RS485 wires… e.g. logic analyzer, but ideally one that collects and logs both analogue and digital.

49

Hi Michael, Is it possible for you to come on remote access to help us enter AT command settings. We tried it at our end but we are not getting ok after multiple attempts. The LoRa device firmware is updated with 1.3a version given by waveshare but in RS232 mode 9600 baud rate - unable to enter AT command settings.

50

I did send you an email last time we discussed.
I am happy to assist and see if I can help, but I need to ensure it does not conflict with my normal job; as such available timeslots to assist will be limited.

I am tinkering with some windows software to try to auto detect the comport settings and then allow you to change the config. Its not public ready yet, but Im happy for people to test on the understanding its not 100% ready/stable.

edit: Can you run some checks for me please?

  1. Turn the device off, what a few seconds then turn it on.
    Do any of the leds come on, come on and go off, or never come on?
  • Normal operation is both leds should flash on and then off to indicate its in normal “pass through” mode.
  1. if you press the “key” button and release, do any of the leds come on/go off ?
  • Normal operation would be for the one of the leds to flash on then off for each press. This action is changing the com port mode from the stored/booted on to the next in the cycle.
    e.g. If the device is hard coded for RS485, then you either need to change the to the correct one you need (e.g. RS232) via the pressing of the key button.
  1. When you try to use the software to talk to the device, do any of the leds come on/go off.
  • Normal operation would be for one (or both) of the leds to flash when in normal mode, and NO flash at all when in AT mode.

If you don’t get any of the normal operations as above, then something is wrong. A re-flash of the firmware should put it back to a default state.