Sercos Communication State Machine and Communication Phases

Overview

The Sercos communication state machine uses the communication state NRT (Non-Real-Time) and five Communication Phases (CP) from CP0 to CP4.

Communication state/communication phase	Description
NRT (non-real-time)	Setup of Ethernet communication First state after power-on or after detected synchronization error Ethernet communication active, master can send and slaves can receive UCC telegrams (store-and-forward or cut-through)
Communication phase CP0	Identification of participating slaves: MDT0 with MST is sent, AT0 acknowledges presence and returns Sercos address
Communication phase CP1	Configuration of slaves for non-cyclic communication via SVC: Master sends MDT0 and MDT1 as well as AT0 and AT1 containing C-DEV controls for slaves (identification, topology) Slaves respond with appropriate status information in their allocated S-DEV controls
Communication phase CP2	Configuration of Sercos communication parameters for CP3 and CP4: Master transmits length of MDTs and ATs with offsets for SVC and RTD of slaves) Communication via SVC Condition for transition to CP3: procedure command S-0-0127 successful
Communication phase CP3	Configuration of application parameters: Structure of MDT complete (offsets for SVC and RDT), configured application data not yet evaluated Condition for transition to CP4: procedure command S-0-0128 successful
Communication phase CP4	Sercos communication active: Sercos communication fully established, bus ready for operation

Transitions to higher communication phases are referred to as “phase-up”, transitions to lower communication phases as “phase-down”.