1.Contact control signal line:
DSR: Data set ready, the data device is ready, indicating that the MODEM is ready for use.
DTR:
Data Terminal ready, the data terminal is ready, indicating that the data terminal can be used.
RTS: Request to send, request to send, used to indicate that DTE requests DCE to send data, that is, when the terminal wants to send data, it makes the signal valid (ON state) and requests MODEM to send. It is used to control whether MODEM wants to enter the sending state.
CTS: Clear to send,
Allowed to send, used to indicate that DCE is ready to receive data from DTE, and is a response signal to the request to send signal RTS. When the MODEM is ready to receive data from the terminal and send it forward, the signal is enabled to notify the terminal to start sending data along the TxD line.
send data.
DCD: Data Carrier dectection, receiving line signal detection, is used to indicate that DCE has connected the communication link and informs DTE that it is ready to receive data. When the local MODEM receives the carrier signal sent by the MODEM at the other end of the communication link (remotely), it makes the RLSD signal valid, notifies the terminal to prepare to receive, and the MODEM demodulates the received carrier signal into digital data. Finally, it is sent to the terminal along the receive data line RxD.
BELL: Ringing indication, when the MODEM receives a ringing call from the switching station
When the signal is generated, make the signal valid (ON state) and notify the terminal that it has been called.
Call.
2Data sending and receiving
TxD: Transmitted data, send data, send serial data to MODEM through TxD terminal, (DTE-DCE).
RxD:
Received data, received data, receives the serial data sent from the MODEM through the RxD line terminal, (DCE → DTE).
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