RS232 signal Definition The RS-232C Standard specifies that 25 interfaces are online. Only the following 9 signals are frequently used. The pins and functions are as follows: 1. txd (2nd feet): sends data lines and outputs. Send the information to the modem. 2. rxd (3rd feet): receives the data line and inputs it. Receive data to a computer or terminal. 3. (4th feet): Send and output requests. The computer uses this pin to notify the modem to send information. 4. (5th feet): Allow sending, input. A computer can send a message only when the answer is correct. 5. (6th feet): Data device ready (that is, modem ready), input. Indicates that the modem can be used, and the signal is sometimes directly connected to the power supply, which is effective when the device is connected. 6. Cd (8th feet): Carrier Detection (receiver), input. Indicates that the modem has been connected to the telephone line. 7. If the communication line is part of the exchange phone, at least two additional signals are required: 8. RI (22nd feet): indicates the ringing, input. If the modem receives a ringing call signal from the switch station, it sends this signal to inform the computer or terminal. 9. (20th feet): The data terminal is ready for output. After receiving the RI signal, the computer sends the signal to the modem as the answer to control its conversion device and establish a communication link. 10. Gnd (7th feet): Signal Location Logic level RS-232C standard using eia level, provisions: The logical level of "1" is-3v ~ -Between 15 V The "0" logic level is in + 3v ~ + 15 V. Because the EIA level and TTL level are completely different, the corresponding level conversion must be performed. The mcl488 completes the conversion from TTL level to EIA level, and the mcl489 completes the conversion from EIA level to ITL level. In addition, maxcompute can complete the level conversion of TTL-> EIA and EIA-> TTL at the same time. In addition to the RS-232C standard, there are some other general asynchronous serial interface standards, such: Standard RS-423A In order to overcome the disadvantages of RS-232C, increase the transmission rate, increase the communication distance, and take into account the compatibility with RS-232C, the American Association of Electronic Industry proposed RS-423A standards in 1987. The main advantage of this standard is that differential input is adopted at the receiving end. Differential input has a high suppression effect on common-mode interference signals, which improves the communication reliability. RS-423A with-6 V represents the logic "1", with + 6 V represents the logic "0", can be directly connected with the RS-232C. Use RS-423A standards to achieve better communication performance than RS-232C. Figure 5-7 shows the rs423a connection. |