BS EN IEC 61158-4-21:2023 - Page 3

Industrial communication networks. Fieldbus specifications. Data-link layer protocol specification. Type 21 elements | Status: Current

1 Scope

1.1 General

The DLL provides basic time-critical data communications between devices in an automated environment. Type 21 provides priority-based cyclic and acyclic data communication using an internal collision-free, full-duplex dual-port Ethernet switch technology. For wide application in various automation applications, Type 21 does not restrict the cyclic/acyclic scheduling policy in the DLL.