about connecting the RS-485 transceiver.

Hi Kiyoshi-san,

For you direct questions:

1. I think adding a inverter is just going to going to add complexities to the system that may cause some issues.

1a) The inverter is another device that will load the bus so its capacitance and impedance must be taken into effect - while logic devices typically wouldn't load the bus that much - my biggest concern is that there could be more impedance mismatches due to the addition of it to the bus which could cause EMI / EMC issues.

1b) The other concern is that the propagation delay between the input and output of the inverter could potentially cause glitches if the delay is too long so that would also need to be a consideration.

1c) It would most likely be easier to tie "B" to mid-VCC so it could operate in a pseudo-differential fashion (as Clemens suggested) however the noise margin will be decreased. Also this solution and the inverter solution will not work in systems with large ground shifts (RS-485 compliant devices can handle a minimum common mode voltage range of -7V to 12V) it will result in either bad data or in the case of the inverter - potential damage/failure. 

2. Z is a driven pin - leaving it floating shouldn't cause any issues with the device; however I'd terminate it to ground with a 375 Ohm resistor (which is the RS-485 defined common mode load) as this pin will still have a voltage associated with it, and a floating pin is much more likely to radiate then if its terminated. 

3. The maximum data rate for the SNx5LBC180 devices is 10Mbps. The above solutions are more likely to cause issues with how long the bus can be - not the datarate so much, so the max data rate should be similar to the 10Mbps - however, depending on how long the bus is in the application is going to determine how fast you can realistically go. Psuedo-Differential setups (using 1-wire) typically do impact how far you can go so speed may degrade in the specific use case.

Clemens' Analysis is correct and he has some good suggestions. 

One part he did mention, the THVD8000, allows for communication signals and power to run on the same bus (with the use of capacitors and inductors to create filters so that the power signal and data signal go to the correct endpoints in the system). I have attached the datasheet, low power design guide, and a high power / low impedance application note so you can see a bit more information about the application - it may be helpful as you are using a system with two wires for power and data which is exactly what this part was made for. 

Data-Sheet: https://www.ti.com/lit/ds/symlink/thvd8000.pdf?ts=1659453656678&ref_url=https%253A%252F%252Fwww.google.com%252F

Low Power (Power Source <= ~30V) Design Guide: https://www.ti.com/lit/an/slla496a/slla496a.pdf?ts=1659453663626&ref_url=https%253A%252F%252Fwww.google.com%252F

HV (Power Source >= ~30V) / Low Impedance Design Guide: https://www.ti.com/lit/an/slla590/slla590.pdf?ts=1659453760561

Please let me know if you have any other questions and  I will see what I can do!

Best,

Parker Dodson