Thanks DavidAlfa for your reply, however I think you've slightly missed the point of my post, even so I've reviewed your answer,
The noise shouldn't be an issue unless you're driving the display remotely through long wires or the pcb layout is terrible.
I2C suffers very much from noise and crosstalk unless you're running tracks shorter than 3 or 4 cm. The tracks have been ground warded, but the inverter switching 6 IGBTs from 0 to 340V in 700ns at 10 kHz injects noise from the switching frequency up to 30MHz. The I2C controller of the CH32V003 is very prone to locking up during the start condition, that combined with the LCD controller weakling driving SCL low, probably due to E field interference, which this controllers are generally very sensitive to, resulting in an interruption of the communications. We ended up having to reset the controller, take controls of SCL and SDA as GPIOs and force them to perform the recovery sequence for the controller (ie START-16 CLK pulses at SDA low-STOP) and reenabling the controller again each time the LCD was refreshed, and since there was no way to know if the data had been indeed received correctly, rewriting the LCD at a rate of 200 Hz so any eventual data corruption would last only 5ms and be unnoticeable. This worked well, but is far from ideal.
The mcu board shoud be shielded to reduce EMI, and if using cables between the mcu and the display, they should be short and also properly shielded.
We are using CH32V003 because we target a very low cost production cost, we don't have the budget for filtering chokes, much less shielding of any kind, only one SMD ferrite to minimise the worst of RF EMI. The system must be noise tolerant, not noise immune. The secondary problem when designing inverters is that the motor chassis and its power cabling shielding, which is required for compliance, are both connected to earth (I'll make a distinction here between earth and ground, since our controller ground voltage is referenced to mains, which earth is not). If we connect any kind of shielding to earth all the noise coming from both motor and power cable will be injected into the cable you're actually trying to protect. If wan't to try and use ground, can't be done because it's at mains potential. If you want to use the secondary double insulated ground, the flyback common mode safety capacitor leaks noise in the frequency of kHz, so you'd have to put in place proper common mode and differential filtering, which we can't afford. So shielding is a no go, even our incremental quadrature encoder, which has cable lengths of up to 25m and uses single ended signals (we can't affort differential transceivers here) has been designed to work reliably with no shielding in any possible environment.
There're plenty of electrically conductive tapes for this task.
Problem is copper is a no go also because this system is used in healthcare and food industry environments, and exposed copper reacts poorly with humidity, moreover there's ingress of disinfection chemicals and gasses with high corrosivity. There's also the problem that the assembly guys refuse to do anything more than the minimal required assembly tasks, they won't even install the compliance output ferrite in series with the motor power cable, so anything that requires extra work outside the engineering department is out of the question, on account of an excess of laziness.
The I2C resistor pullups can be lowered to 1K or 470R for further noise resistance.
I won't say that's always a mistake, but I'm quite certain that's always a mistake. I don't know how started that myth about I2C and lowering pull-up resistors. It's highly unlikely that your coupled noise equivalent output impedance is in the range of less than 1K unless you're running an insanely long I2C bus. Lower pull-up resistors were mandated by higher clock frequencies to overcome the capacitance of the bus tracks, but that has severe drawbacks, that results in larger rising edge slew rate, which most of the time results in higher crosstalk, it's true that the worst case scenario should be rising edge agains open collector pulled up line which shouldn't result in data corruption, but in reality, just with 5cm of unguarded tracks and 2.2K pull-ups I've been able to capture data flipping from 0 to 1 at the receiving side, so it's better to stick with the regular 4.7K resistors and either keep your buses short, slow and guarded, or if you can't avoid it because you need the speed and your capacitance is high, go no further down 2K and design your PCB with the utmost care including series resistors for every bus driver so that falling edges have controled slew rate, which is in fact one of the greatests noise sources on any I2C bus.
Best regards
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