Profibus System Integration PDF 4.03MB - Schneider Electric

Segment Coupler.Profibus DP - RS 485-Asynchronous NRZ coding-1 byte requires11 bit (1 start + 8bit + 1 stop + 1 parity)-Transmission rate: 9.6 kbit/s to 12Mbit/sSegmentCouplersDPPAProfibus PA - MBP-Synchronous Manchester II coding-1 byte requires 8 bit-Transmission rate 31.25 Kbit/sA Transparent Segment Coupler acts as a kind of transparent gateway, whichconverts the asynchronous 11-bits/byte DP protocol into the 8-bits/byte synchronousPA protocol. This means that PROFIBUS queries, (generated by the Master PLC orthe Asset Management station, for example) are routed, without any specifictreatment, directly to PROFIBUS PA devices. Responses from these devices are inturn routed directly back to the device which generated of the Profibus query.The only distinction between PROFIBUS DP and PROFIBUS PA are any requiredadaptations, implicitly handled, based on differences with the Data Link or Physicallayer; everything else remains identical.The main benefit is that no particular configuration is required to setup the Coupler. ATransparent Segment Coupler offers full access to the PROFIBUS PA devicesbelonging to the segment it drives. This gives the Master the ability to cyclicallyaccess up to 244 Input bytes and 244 Output bytes from any PROFIBUS Slave, anddoes not require any PROFIBUS address.Most manufacturers that offer Transparent Segment Couplers provide two distincttypes:• The first type of Transparent Segment Coupler is designed to interfacePROFIBUS PA devices installed in a non explosive area. The segment coupler istypically able to drive a PROFIBUS PA segment counting up 31 devices.• The second type of Transparent Segment Coupler is designed to interfacePROFIBUS PA devices installed in an explosive area. The segment coupler isgenerally compatible with devices featuring an intrinsic safety protection method(Ex ia/ib). In these conditions, the major drawback is the current limitationimposed by the potential explosion risk (typically 10 mA per device stub, andapproximately 100 mA on the trunk line).26