BECKHOFF FC7501 - Manual (Page 6)

Product Overview
6 FC750x
2. Product Overview
System description
SERCOS is an open, fast bus system that has been the international standard (IEC 61491) for numerically con-
trolled machines since 1995. Meeting high real-time requirements and interference-proof transfer in optical fiber
technology are important features of this bus system, which is widely used for drive technology applications. The
bus consists of a master and of a number of slaves. In a SERCOS system, the servo drives or the BK7500 SER-
COS Bus Coupler represent the slaves.
The bus topology is a ring system, in which it is possible to operate up to 254 stations. The transmission speed is
2, 4, 8 or 16 Mbit/s. There are basically three types of telegram:
1. The master-sync telegram is received by all the slaves, and is used for synchronisation.
2. The master data telegram is also received by all the slaves, and contains the cyclic data and the service
data.
3. The slaves send their data in the form of a drive telegram.
PC Fieldbus Cards for SERCOS Interface
Beckhoff specially developed the fieldbus cards FC7501 (single-channel) and FC7502 (double-channel) with PCI
interface for the SERCOS interface. The driver integrated in the TwinCAT automation software ensures optimum
performance of these passive master cards, so that compared with an active solution there are no unnecessary
restrictions with regard to the number of devices or the data length. This also enables larger SERCOS projects
with more than 50 axes to be realised. To do so several PCs are precisely synchronised via SERCOS, whereby
one PC is defined as the master and all the others as slaves. For these applications it is interesting that the
FC7502 double-channel card can handle one master ring and one slave ring. The parameterisation of the mas-
ter/slave mode is carried out simply through the software.
Bus Coupler for SERCOS interface
A further advantage results from the use of Beckhoff Bus Terminals with the BK7500 SERCOS Bus Coupler,
which enables the high data rate, short cycle time and high deterministic features of SERCOS also to be used for
classic I/O technology. Up to 64 the Bus Terminals for different analog or digital signals can be coupled to a single
Bus Coupler. Machine manufacturers with a high drive consumption and low I/O consumption no longer have to
install an additional I/O bus.
SERCOS control system
With TwinCAT as software PLC/NC, SERCOS cards, digital servo drives and Bus Terminals as I/O system, Beck-
hoff thus provides a complete PC-based control system for the SERCOS interface.