6.6.2 FC/SFC 218 - SER_RCV - Receive from PtPThis block receives data via the serial interface. Using the FC/SFC 218 SER_RCV afterSER_SND with the protocols USS and Modbus the acknowledgement telegram can beread.More information about the usage of these blocks may be found in themanual "SPEED7 Operation List" from VIPA.6.7 Protocols and proceduresThe CPU supports the following protocols and procedures:n ASCII communicationn STX/ETXn 3964Rn USSn ModbusASCII data communication is one of the simple forms of data exchange. Incoming char-acters are transferred 1 to 1. At ASCII, with every cycle the read FC/SFC is used to storethe data that is in the buffer at request time in a parametrized receive data block. If a tele-gram is spread over various cycles, the data is overwritten. There is no receptionacknowledgement. The communication procedure has to be controlled by the concerninguser application. For this you can use the FB 1 - Receive_ASCII.More information about the usage of this block may be found in themanual "SPEED7 Operation List" from VIPA.STX/ETX is a simple protocol with start and end ID, where STX stands for Start of Textand ETX for End of Text.n Any data transferred from the periphery must be preceded by a Start followed by thedata characters and the end character. Depending of the byte width the followingASCII characters can be transferred: 5bit: not allowed: 6bit: 20...3Fh, 7bit: 20...7Fh,8bit: 20...FFh.n The effective data, which includes all the characters between Start and End are trans-ferred to the CPU when the End has been received.n When data is send from the CPU to a peripheral device, any user data is handed tothe FC/SFC 217 (SER_SND) and is transferred with added Start- and End-ID to thecommunication partner.n You may work with 1, 2 or no Start- and with 1, 2 or no End-ID.n If no End-ID is defined, all read characters are transferred to the CPU after a parame-terizable character delay time (Timeout).As Start-res. End-ID all Hex values from 01h to 1Fh are permissible. Characters above1Fh are ignored. In the user data, characters below 20h are not allowed and may causeerrors. The number of Start- and End-IDs may be different (1 Start, 2 End res. 2 Start, 1End or other combinations). For not used start and end characters you have to enter FFhin the hardware configuration.Message structure:OverviewASCIISTX/ETXVIPA System SLIO Deployment PtP communicationProtocols and proceduresHB300 | CPU | 013-CCF0R00 | en | 19-30 175
