Practical Industrial Data Networks:Design, Installation and ...

146 Practical Industrial Data Networks: Design, Installation and Troubleshootingprovide for rapid, positive device attachment to the AS-i flat cable. Provision is made inthe communications system to make ‘live’ connections, permitting the removal oraddition of nodes with minimum network interruption.Connection to higher level networks (e.g. ProfiBus) is made possible through plug-inPC and PLC cards or serial interface converter modules.The following sections examine these features of the AS-i network in more detail.11.2 Layer 1 – the physical layerAS-i uses a two-wire untwisted, unshielded cable that serves as both communication linkand power supply for up to thirty-one slaves. A single master module controlscommunication over the AS-i network, which can be connected in various configurationssuch as bus, ring, or tree. The AS-i flat cable has a unique cross-section that permits onlyproperly polarized connections when making field connections to the modules.Alternatively, ordinary 2-wire cable (#16 AWG, 1.5 mm) can be used. A special shieldedcable is also available for high noise environments.STARMasterLINE WITHLAYER SWITCHESMasterLINEMasterTREEMasterFigure 11.1Various AS-i configurations