OPC - OLE (Object Linking and Embedding) for Process Control :: The Industrial Interoperability Standard
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DH+ is Data Highway Plus Industrial Local Area Network from AB.
The Data Highway Plus (DH+) network is a local area network that is very simple to implement. It is designed to provide simple communication between AB's PLCs, SLCs and PCs.
The Data Highway Plus network allows connection to a maximum of 64 devices per link (although 15 or fewer nodes are recommended per link), including: