SLLA660 December   2024 THVD1400 , THVD2410

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Overview of RS-485
  6. 3 Shorting DE and nRE Pins
  7. 4 General R Pin Glitch Background
  8. 5 Theoretical Glitch Case for RS-485 Transceivers
  9. 6 Theoretical THVD24XX Idle Fail-safe Case
  10. 7 RS-485 Testing Setup
  11. 8 THVD1400 Capacitance Results
  12. 9 THVD2410 Capacitance Results
  13. 10Voltage Drop Workarounds
  14. 11Summary
  15. 12References

2 Overview of RS-485

RS-485 is a standardized, physical layer communication method. Standardized by the Telecommunications Industry Association (TIA) and Electronic Industries Alliance (EIA), RS-485 defines the electrical characteristics of a multi-point differential system. This provides designers with improved noise immunity, data rates up to 50Mbps, and the capability to transmit over 1.2 km at 100kbps or less with multiple transceivers on the bus. Figure 2-1 demonstrates a typical setup with a half-duplex RS-485 transceiver.

Typical RS-485 Half-duplex Setup with nRE and DE Shorted Figure 2-1 Typical RS-485 Half-duplex Setup with nRE and DE Shorted

A microcontroller can send and receive data using a variety of protocols since RS-485 only defines the physical layer. In the transmit mode, the transceiver receives data through the D pin from the MCU. The transceiver can then output dominant and recessive values to the bus via the differential outputs: A and B. A is typically the non-inverting bus line, while B is the inverting bus line. In receiving mode, the transceiver can output a digital signal to the R pin by reading the difference of the A and B bus lines.