A LOTOS Specification of the SERCOS Fieldbus Protocol

This paper presents the modelling of the SERCOS field-bus protocol using the standard formal description technique LOTOS. SERCOS is a strictly synchronous field-bus protocol and it is used in order to connect a master with several slaves by using a ring topology network. After a brief informal description of the protocol main features, the various problems found in developing the LOTOS specification are addressed. The paper also shows how network configurations can be specified in LOTOS by using simple building blocks. Each building block is well explained and the way to obtain new blocks from the ones presented is also shown. Tinting aspects, which are essential in field-bus protocols, are dealt with by means of timeticks, since standard LOTOS does not cater for specific constructs for this purpose. The global network synchronism is achieved by means of a LOTOS globalevent which enforces a synchronization after each network operation.