SLLA628 September   2023 THVD1424

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Use Case Domain of RS-485
    1. 1.1 RS-485 Compliant Transmitter
    2. 1.2 RS-485 Compliant Receiver
    3. 1.3 RS-485 Transceiver Use Case Variability
  5. 2Traditional RS-485 Design Process
    1. 2.1 Design Process Overview
    2. 2.2 Requirement Definition
      1. 2.2.1 Bus Voltage and Logic Voltage (VCC and VIO):
      2. 2.2.2 Number of Communication Nodes Supported plus Static vs. Dynamic Systems
      3. 2.2.3 Max Bus Length, Network Topology, Emission Concerns, and Data Rate Required
      4. 2.2.4 Duplex
      5. 2.2.5 Protection Needs
      6. 2.2.6 Additional Features of RS-485 Bus
    3. 2.3 IC Selection, Application Design, and Validation/Qualification
  6. 3One Multi-System Design: Flexible RS-485 with the THVD1424
    1. 3.1 Flexible Multi-System Design
    2. 3.2 Simplification of RS-485 Design Process Using THVD1424
      1. 3.2.1 Bus Voltage and Logic Voltage Supplies (VCC and VIO)
      2. 3.2.2 Number of Communication Nodes Supported plus Dynamic or Static Systems
      3. 3.2.3 Max Bus Length, Network Topology, Data Rate, and Emissions Concerns
      4. 3.2.4 Duplex
      5. 3.2.5 Protection Needs
      6. 3.2.6 Additional Features
  7. 4Summary
  8. 5References

2.2.2 Number of Communication Nodes Supported plus Static vs. Dynamic Systems

A designer must know how many communication nodes will need to be supported in the system – as this will define the minimum unit load fraction of a device. One important caveat for designers to consider is if the system is static or dynamic- meaning is it possible for nodes to be removed or added over the life time of the system’s design? Consider an HVAC system the is originally designed for 32 units and the designer selected a 1 Unit Load RS-485 Transceiver for the wired communication in the system. Now imagine the HVAC system needs an update which will require the support of 18 additional units, this would require a redesign as 1 Unit Load devices will not be able to support a bus with 50 devices. So a designer must consider if additional nodes are possible when the original system design is conceived to avoid future redesigns and IC selections. The dynamic system could also change which nodes are terminated in a system so multiple designs may exist for the same use case.