RS-232C protocol interface signal

We know that the use of RS-232C protocols is well-developed in some areas of electrical and mechanical, and the basics of this are also described in previous articles. So as a supplement, we next to the RS-232C protocol interface signal to a comprehensive summary. I hope this will help you.

RS-232C protocol standard interface has 25 lines, 4 data lines, 11 control lines, 3 scheduled lines, 7 standby and undefined lines, commonly used only 9, they are

RS-232C protocol interface signal (1)

Contact control signal line:

Data set ready-DSR (ON) status indicates that the MODEM is in usable status ｡

Data set ready-DTR (ON) status indicates that the Data terminal can be used ｡

These two signals are sometimes connected to the power supply, and are immediately effective upon power-on. The status signals of these two devices are valid, only indicating that the device is available, but not that the communication link can start to communicate, the following control signal determines whether communication can start ｡

Request to send-RTS (Request to send-RTS) -- indicates that the DTE Request sends data to the DCE, that is, when the terminal wants to send data, this signal is valid (ON status ), send a request to the MODEM. It is used to control whether the MODEM is going to be sent ｡

Clear to send-CTS (Clear to send-CTS) -- indicates that the DCE is ready to receive data from the DTE and is a response signal to the request to send the RTS. When the MODEM is ready to receive data from the terminal, this signal is valid when it is sent forward, and the notification terminal starts to send data along the TxD data line ｡

This contact signal is used for switching between the sending and receiving modes in the half-duplex MODEM system. switching between the sending and receiving modes is performed in the full-duplex system. medium, because two-way channel is configured, you do not need the RTS/CTS contact signal to increase it ｡

Receive Line Signal detection (RLSD)-used to indicate that the DCE has been connected to the communication link and inform the DTE to prepare for receiving data. When the local MODEM receives the data, the other end of the communication link (far away) make the RLSD signal effective when the MODEM sends the carrier signal, notify the terminal to prepare for receiving, and after the MODEM decrypts the received carrier signal into digital data, this line is also called the Data Carrier dectection-DCD line ｡

Ringing-RI-when the MODEM receives the Ringing call signal sent by the switching station, make the signal valid (ON status), the notification terminal, has been called ｡

RS-232C protocol interface signal (2)

Data transmission and receiving lines:

Transmit data (Transmitted data-TxD)-send serial data to the MODEM (DTE transmit DCE) through the TxD terminal )｡

Receive data (stored ed data-RxD)-receives serial data from the MODEM through the RxD line terminal (DCE distributed DTE )｡

RS-232C protocol interface signal (3)

Ground:

There are two lines SG and PG-signal ground and protected line, with no direction ｡

When the above control signal line is valid, and when the order is invalid represents the interface signal transmission process. For example, only when the DSR and DTR are in the valid (ON) status, in order to transfer data between DTE and DCE. If DTE wants to send data, set the DTR line to the ON status in advance and wait for the CTS to receive the ON status) after the status is answered, the serial data can be sent on the TxD line. This sequence is particularly useful for half-duplex communication lines, because half-duplex communication can determine that the DCE has changed from the receiving direction to the sending direction, then the line can start sending ｡

Two data signals: TXD and RXD ｡

One signal ground line: SG ｡

Six control signals:

DSR & #0; & #0; digital transmitter (modem) Ready, Data Set Ready.

DTR & #0; & #0; Data Terminal (DTE, that is, microcomputer interface circuit, such as Intel8250/8251,16550) Ready, Data Terminal Ready ｡

RTS & #0; & #0; DTE Request DCE sends (Request To Send )｡

CTS & #0; & #0; DCE allows DTE To Send. This signal is an answer To the RTS signal ｡

DCD & #0; & #0; Data Carrier Detection, Data Carrier Detection when the local DCE device (Modem) receives the Carrier signal sent by the recipient's DCE device, make DCD valid, notify DTE to prepare for receiving, and the DCE will demodulated the received carrier signal into a digital signal, and send it to the DTE through the RXD line ｡

RI & #0; & #0; Ringing signal Ringing: When DCE receives the Ringing call signal sent by the switch, this signal is valid, notifying DTE that it has been called.