7.5 Communication7.5.1 FC/SFC 217 - SER_SND - Send to PtPThis block sends data via the serial interface. The repeated call of the FC/SFC 217SER_SND delivers a return value for 3964R, USS and Modbus via RETVAL that con-tains, among other things, recent information about the acknowledgement of the partnerstation. The protocols USS and Modbus require to evaluate the receipt telegram bycalling the FC/SFC 218 SER_RCV after SER_SND.7.5.2 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.7.6 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 parameterized receive data block. If atelegram is spread over various cycles, the data is overwritten. There is no receptionacknowledgement. The communication procedure has to be controlled by the concerninguser application. An according Receive_ASCII FB may be found within the VIPA library inthe service area of www.vipa.com.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).OverviewASCIISTX/ETXVIPA System MICRO Option: PtP communicationProtocols and proceduresHB400 | CPU | M13-CCF0000 | en | 16-47 161
