Hi Toto,
My opinion without any evidence to back it up is that it is a hardware problem rather that software. Transients can really spoil your day.
I say this with a background of using RS485 for networking Fire Indicator Panels and Emergency Warning Panels over a wide variety of installation environments. Everything from Sydney Airport to Parliament House, to power stations and mines with 3+ km runs. The hardware failure and data error rates are very low.
So, the tricks employed are:
1. Use shielded cable. Twisted if you can get it. This adds to the cable capacitance, but helps keep the garbage at bay.
2. Connect all the shields together, but only Earth (or connect to 0V) at one point. Preferably the master.
3. Provide transient protection to the RS485. Series 10R resistors for the D+ and D-, inductive filters MOVs and Transorbs.
4. This one is a contentious one: provide pull up (2K7) / balance (470R) / pull down (2K7) resistors for D+ and D-. Some data sheets say only provide these on the ends of runs, but I have seen this arrangement run over 2 km with 35 devices.
5. Make sure the power supply to the board is clean. I use a bifilar would toroid. This stops everything. Put the processor board next to a fluoro desk lamp and turn the lamp off and on a few times. If the board resets, filter the supply.
Don't try to save a few bucks by skipping this stuff. The cost of not doing it is ongoing pain as well as dollars.
Just my 2c.
Cheers,
Tony
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