You can freely build on How Self-Healing Data Loops Automatically Elect a New Master Controller
This patent expired in 2004. Every claim — 0 independent, 1 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Process Systems Inc
Patent granted
1987
Expired
2004
Forward citations
83
What this patent covers
This patent describes a network of devices connected in a loop where every device is capable of acting as either a 'master' or a 'slave'. The master node provides the master clock, which keeps all other nodes (slaves) synchronized so they can pass data reliably. If the master node fails or is removed, the other nodes detect the silence and use a timing mechanism to decide which one will become the new master. This allows the network to stay operational without manual intervention, effectively creating a self-healing communication loop.
What is now free to use
All 1 claims of US 4677614 are in the public domain. Specifically:
The 1 dependent claim add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
Does not cover networks that rely on a central server that cannot be replaced by a node.
Does not cover non-synchronous communication systems that do not use a master clock.
Does not cover systems where the master node is fixed and cannot be reassigned to another node.
Who is building on this today
The principles of master-slave election and fault-tolerant loops are now standard in industrial automation protocols like EtherCAT and various fieldbus technologies. Companies like Siemens, Rockwell Automation, and Beckhoff utilize similar logic to ensure high availability in their control networks.
Products built on expired version of this technology
Token ring network architectures
Industrial fieldbus communication systems
Redundant serial data loops in factory automation
How to cite this patent in your documentation
Process Systems Inc. US Patent 4677614. Data communication system and method and communication controller and method therefor, having a data/clock synchronizer and method. Granted 1987, expired 2004. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.