Communication with the double device profile (B device)

The double device combines 2 independent devices in one drive. The A device controls the drive via cyclic data exchange. Parameter communication with the inverter can be realized via the B device. Cyclic drive control and acyclic parameter communication via the 2 devices are independent of each other.

The CTT2 service of the AS-Interface is used as the transport layer for parameter communication. The Smart Parameter Access protocol (SPA), which was specifically developed by SEW‑EURODRIVE for the inverters of the MOVI-C® modular automation system, is attached to this service with the parameter access information as a 12 byte data packet:

CTT2 protocol (1 – 4 bytes)

SPA protocol (12 bytes)

Transfers the attached data of the SPA protocol between the AS-Interface master and the AS-Interface device.

The specific protocol from SEW‑EURODRIVE contains information regarding access to inverter parameters.

The AS-Interface master transmits the entire data packet to the B device via the CTT2 service. The B device interprets the SPA protocol, executes the desired parameter access to the inverter and sends the result of the parameter access back to the AS-Interface master:

  • either via the CTT2 Data Exchange Request/Response service and attached SPA protocol
  • or via another CTT2 Write Request/Response and/or Read Request/Response service

In the case of the CTT2 Data Exchange Request/Response service, the device automatically responds to the Data Exchange Request via the Data Exchange Response.

In the case of the CTT2 Write Request/Response and Read Request/Response service, the device must be queried cyclically via the Read Request until it can provide the parameter value in the Read Response. In addition to the increased implementation effort in the control system, this also slows down parameter communication.

SEW‑EURODRIVE recommends using the CTT2 Data Exchange Request/Response service for parameter communication.

Additional information