Home Page | HCA Main Page | Contact us

red_button.gif (982 bytes) HCA: Network Examples

RS-484 network with HW4 PC

When the RS-485 network is connected to a HW4 PC, via a master, the HW4 PC takes over the task of sending data requests and instructions to the different units on the RS-485 network. Each unit remains silent unless interrogated by the PC.

As long as the polling interval of the HW4 PC is set to 1 minute or less, the HCA remains silent unless interrogated by the HW4 PC (passive mode). In the passive mode, the HCA listens to the data sent by the instruments that it is programmed to monitor.
RS-485 network without HW4 PC (no PC or PC crash)

The HCA switches automatically to the auto-polling mode in the following situations:

  • The polling interval of the HW4 PC is set to more than 1 minute

  • The HW4 PC is disabled

  • No PC is connected to the RS-485 network

In the auto-polling mode, the HCA takes over the task of polling the instruments that it is programmed to monitor. The polling interval is 10 seconds. When several HCA are connected to the same RS-485 network, each HCA does its own auto-polling, one HCA at a time.