Profibus DP Communications
ORMEC provides Profibus connectivity to the ORION motion controllers by using a standard Profibus communications adapter and a MotionBASIC Extension (MBX) to implement either Profibus DP Master or Slave communications. Connectivity to the ORION controller provides the machine developer with a modern approach to machine control networking using Profibus DP communications.
Features and Benefits
Advantages of using Profibus DP communications:
- Factory connectivity: Profibus DP provides a convenient way to integrate ORION with PLCs or PCs running HMI or soft PLC programs and using open Profibus DP network for distributed I/O.
- High-speed and cost-effective: A standard Profibus adapter provides performance up to 12 Mbits/sec using a master-slave protocol with up to 126 nodes.
- Minimal impact on MotionBASIC program execution speed: Once initialized, Profibus communications between the Master and Slave(s) runs as a background task controlled by a processor on the Profibus Adapter, minimizing application program complexity and workload on the ORION controller.
Profibus is a vendor independent, open fieldbus standard for a wide range of applications in manufacturing. Vendor independence and openness are guaranteed by the Profibus standard EN 50170. With Profibus, a developer provides uniformity between different manufacturers' devices by using a fast and efficient communications protocol. Profibus can be used for both high-speed time critical data transmission and extensive, complex communication tasks without interface modifications. High-speed, time-critical data transmission at the fieldbus level is defined by the Profibus DP specification.
Profibus DP Bus Interface
The combination of a Profibus Communications Adapter and Profibus MBXs gives an ORION motion controller Profibus DP Master or Slave functionality. Slaves on a Profibus DP bus appear as I/O drops with up to 244 bytes of inputs and 244 bytes of outputs each. The inputs and outputs can be divided between bit data and 16-bit word data. The word data is used to pass system parameter and status information between the Slave and a Profibus DP Master.
Profibus DP Architecture
Profibus DP defines the technical and functional characteristics of a serial Fieldbus which interconnects distributed digital field devices in the low (sensor/ actuator level) up to the medium (cell level) performance range. The basic system architecture consists of one or more master devices and one or more slave devices. Any master device can control the bus. When it has the right to access the bus, a master will transfer messages without waiting for a remote request. Slave devices are peripheral devices that have no bus access rights - i.e. they may only acknowledge received messages or, at the request of a master, transmit messages.
Profibus DP Configuration
A network configuration program and device configuration file (*.GSD) are supplied with the Profibus adapter. The device configuration file is used by the network configuration program to create the configuration data file that is read by the DP Master. The device configuration file tells the network configuration program what the capabilities of the node are and whether the user can choose how much data to transfer. In the case of a simple solenoid bank or proximity sensor, the amount of data available from the node is predetermined and fixed. In the case of a configurable node the user can program the amount of data the node is able to exchange.
In either case, each slave device needs a configuration data file to use at initialization time to know how the node will present its data on the network and how many inputs and outputs each node will have. The Profibus Communications adapter used with ORION as a DP Slave provides this type of configurable node. Network configuration file (netslv.ncf) and a slave configuration file (slave.scf), modified by the user, tell the Profibus DP Slave MBX driver how to split up 244 bytes of input data and 244 bytes of output data between bits and words, how many bytes of inputs and outputs are being transferred, its node address and the baud rate of the card. The PFB.DUMP commands and PFBLOG.TXT file to verify installation.
The Profibus Communications adapter used with an ORION as a DP Master uses the configuration data file to initialize all the configurable nodes on the network at startup. The configuration data file also tells the Profibus DP Master MBX how much of each data type to read from each DP Slave node.
The Profibus communications MBX uses the adapter installed in the ORION ISA bus backplane. Two LEDs on the card provide system status and bus network status indications. The bus interface is a 9-pin D-sub connector. A Siemens 6GK1500-0FC00 (or equivalent) is included with the Profibus Adapter. No special tools or soldering is required to attach the Profibus Cable to the Siemens 9-pin connector.
The recommended cable is Belden Profibus Cable 3079A. A Profibus network must be terminated at devices located at each end. Siemens 9-pin cable connectors have switches in their shell to turn the terminator on and off. The default bus transfer rate is set at 12M bps. Scan rates are dependent on the total number of inputs and outputs on all nodes of the bus.