Ring Operation

HIDAS™ Node boards/Backplanes are connected serially to and from the system’s Host Interface Controller (HIC) forming a ring. Each Node board in the ring uses a token ring style protocol to provide a deterministic data rate on the bus.


Messages originate from software and are transmitted to the first Node board in the ring via the HIC.


  • If the message is addressed to this node, the node responds to the command in the message, modifies the message as required, and re-transmits the message to the next node in the ring.
  • If the message is not addressed to a Node board, then it transmits the message on to the next Node board without modification

A message ultimately makes its way completely around the ring and back to the HIC, where the HIC moves the collected data and status into shared memory for application software use.


The HIDAS™ interface software includes built-in test functions that execute when HIDAS™ is initialized. The built-in test verifies ring continuity and link controller memory integrity.


Each Node board has one or more LEDs to indicate power on and data clock received from the transmission link. If the ring breaks or a Node board fails, subsequent boards will self generate a data packet after a period of no inbound activity. This feature, in conjunction with the LEDs, allows fault isolation to one of two boards. Using diagnostic software on the host PC, a technician can quickly isolate a fault to a specific board or attached component.

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