6.2 Principle of the data transferThe data transfer is handled during runtime by using FC/SFCs. The principle of datatransfer is the same for all protocols and is shortly illustrated in the following.n Data, which are written into the according data channel by the CPU, is stored in aFIFO send buffer (first in first out) with a size of 2x1024byte and then put out via theinterface.n When the interface receives data, this is stored in a FIFO receive buffer with a size of2x1024byte and can there be read by the CPU.n If the data is transferred via a protocol, the embedding of the data to the accordingprotocol happens automatically.n In opposite to ASCII and STX/ETX, the protocols 3964R, USS and Modbus requirethe acknowledgement of the partner.n An additional call of the FC/SFC 217 SER_SND causes a return value in RetVal thatincludes among others recent information about the acknowledgement of the partner.n Further on for USS and Modbus after a SER_SND the acknowledgement telegrammust be evaluated by a call of the FC/SFC 218 SER_RCV.1 Program2 Protocol3 FIFO buffer4 InterfaceRS485 PtP communicationVIPA System 300S+ Deployment PtP communicationPrinciple of the data transferHB140 | CPU | 317-2AJ23 | en | 17-25 79
