• RS485 Polarity Issues

    RS485 is an electrical communication standard used by Modbus­RTU, BACnet­MSTP, and many other building automation protocols. This article covers issues related to the polarity of the RS485 differential balanced line. A differential balanced line consists of two wires (negative and … Continue reading

  • USB-COMi-SI-M USB-to-Optical isolated RS-422/485 Adapter

    Wiring diagram RS485. [USB-COMi-SI-M, pin 1]  (-) Negative [USB-COMi-SI-M, pin 2]  (+) Positive [USB-COMi-SI-M, pin 5]  Ground [USB-COMi-SI-M, Sw1] OFF [USB-COMi-SI-M, Sw2] OFF [USB-COMi-SI-M, Sw3] ON [USB-COMi-SI-M, Sw4] ON Driver Downloads Download USBCom-CDM

  • Useful tools and applications for Modbus

    Here’s a useful list of tools to use with Modbus devices: CAS Modbus Scanner (download) Allows us to retrieve coils, inputs, holding registers, and input registers from a Modbus enabled device. Modbus RTU Parser (download) Allows us to analyze an … Continue reading

  • CAS Modbus Scanner v1.02aB

    CAS Modbus Scanner is a utility to retrieve coils, inputs, holding registers, and input registers from a Modbus enabled device. Values retrieved from the device can be viewed in many different formats including Binary, HEX, Uint16, Int16, Uint32, Int32, and … Continue reading

  • RS485 on a Scope

    Using an oscilloscope on a RS485 network. For reference purposes we present some scope captures of a typical RS485 line. In this capture we had our scope leads connected to the positive signal conductor and ground. Zone A: Idle State … Continue reading

  • CAS Modbus Explorer

    Modbus communications not working ? How do you know what’s wrong – is it the baud rate, the parity or even the address? There are so many things that can affect communications. The Modbus protocol does not support discovery. There … Continue reading

  • Reducing latency on com ports

    When a BYTE is sent from a serial device (BACnet MSTP thermostat) to a USB to 232/485 converters (USB-COMI-SI-M) it is cached on the USB converter until one of two things happened. Transfer size – More then x BYTES are … Continue reading