RS232 hardware handshake protocol - Solutions - Huaqiang Electronic Network

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Under normal circumstances, RS232 communication only needs three lines plus a perfect protocol to complete the communication. Especially for the serial port with DMA function or multi-level hardware FIFO buffer, it is a piece of cake to work under full duplex. However, this use is limited for the case where the receiver is overloaded. At this time, the serial port handshake function is required.
Hardware Handshake: In addition to the Tx and Rx data lines, RTS/CTS and DTR/DSR work together, one as an output and the other as an input. The first set of lines are RTS (Request to Send) and CTS (Clear to Send). When the receiver is ready to receive data, it sets the RTS line high to indicate that it is ready. If the sender is also ready, it sets CTS high to indicate that it is about to send data. The other set of lines is DTR (Data Terminal Ready) and DSR (Data Set Ready). These are now mainly used for modem communication. Enable the serial port and modem to communicate their status. For example, when the modem is ready to receive data from the PC, it sets the DTR line high, indicating that the connection to the phone line has been established. The read DSR line is set high and the PC starts transmitting data. A simple rule is that DTR/DSR is used to indicate that the system is ready for communication, while RTS/CTS is used for the transmission of a single packet.