As TI employees, we are often asked if there are any insights or tips we have when designing with RS-485. To this end, we have compiled a series of comprehensive tips that must be remembered when using RS-485.
And usage methods……
1) Use twisted pair cables with Zo = 120Ω or 100Ω
2) Connect bus nodes in a daisy chain
3) Terminate unused conductors of RT = Z0 to their local ground
4) Terminate one end of the cable at RT1 = Z0
5) Apply fail-safe biasing at the other end of the cable
6) Terminate that end
7) Determine the maximum cable length based on the figure in the lower right corner
8) Ensure the length of the terminals does not exceed
9) You can use both 3V and 5V devices on the same bus
10) Use SM712 for ESD, EFT, and surge protection
11) Use a 10Ω pulse or MELF resistor to limit the clamping current entering the transceiver
12) Use an R-C low-pass filter (fc ≥ 5 x DR) to filter signal noise between the transceiver and UART
13) For ± 7V GPD, use a standard transceiver
For ± 20V GPD, use SN65HVD17xx
For higher GPD, use an isolated transceiver
