The communication mechanism of the RS-232 standard interface

What are the RS-232 standard interface, LS2208 RS232 cable, and barcode scanner RS232 cable both need to use this excuse? The following is the communication process between the computer and modem to explain the RS-232 serial communication principle. Consider the interaction between the RS-232 signals and the working process between the computer and the modem when the modem is in the answer mode. Assume the modem is a full duplex and works with RS-232 standard specifications.

(1) In the initial state, RTS and CTS are ON continuously, and the RS232 lead status is set and monitored by the communication program. In the answer mode, the software in the computer keeps monitoring the ringing indication (RI) and waiting for the RI to signal ON.

(2) After receiving the RI signal, the communication program on the computer starts to count the ringing by the number of ringing indicator ON/OFF transitions. When the program sets the number of ringing, the communication program generates the data terminal ready (DTR) signal, forcing the modem to enter the off-hook state.

(3) After waiting for 2s (as specified by FCC), the modem automatically sends its answer carrier. The modem sends a ready (DSR) signal to inform the computer that it has completed all preparations and is waiting for the carrier signal.

(4) The computer software monitors the DSR signal during the continuous DTR signal. When the DSR signal turns ON, the computer knows the modem is ready for the data link connection. The computer immediately starts monitoring the data carrier monitoring (CD) signal to confirm the presence of the data link.

(5) When the carrier of the source modem appears on the telephone line, the answering modem sends a CD signal.

(6) Full-duplex communication begins through the transmit data line (TD) and the receive data line (RD). During the data link transmission, the computer ensures the presence of the data link by monitoring the CD.

(7) Once the communication task is complete, the computer disables DTR, and the modem responds by removing its carrier tone and disabling CD and DSR. As the link is removed, the modem returns to its initial state.

RS-232 serial communication distance is close (<12m). You can use the cable directly connected to the standard RS232 port. If the distance is far needed to attach the modem ( Mode), the most simple and commonly used is a three-wire system connection: ground, receive data, and send data three pins connected.