The Max-232 IC is started by the maxim integrated products in 1987. It is an integrated circuit which converts the signals from the RS232 serial port to the proper signal which are used in the TTL compatible digital logic circuits. The MAX232 can convert the signals like RX, TX, CTS, and RTS and it is a dual driver/receiver. The driver increases the output voltage levels of TIA232 from a 5 volt supply to 7.5 volts by using the external capacitor and on chip charge pumps. The receiver reduces the input levels of the TIA232 from 25 volts to the standard voltage level, i.e. 5volts of TTL levels and there is a threshold of 1.3 volts and hysteresis of 0.5 volts for the receiver. Further the max232 IC is extended by the four receivers and transmitters simultaneously with eight receivers and transmitters which are MAX238 and MAX248 and there are many combinations of receivers and transmitters.
The pin description for the RS-232 pins is as follows:
DTR (data terminal ready): When terminal is turned on, it sends out signal DTR to indicate that it is ready for communication.
DSR (data set ready): When DCE is turned on and has gone through the self-test, it assert DSR to indicate that it is ready to communicate.
RTS (request to send): When the DTE device has byte to transmit, it assert RTS to signal the modem that it has a byte of data to transmit.
CTS (clear to send): When the modem has room for storing the data it is to receive, it sends out signal CTS to DTE to indicate that it can receive the data now.
DCD (data carrier detect): The modem asserts signal DCD to inform the DTE that a valid carrier has been detected and that contact between it and the other modem is established.
RI (ring indicator): An output from the modem and an input to a PC indicates that the telephone is ringing. It goes on and off in synchronous with the ringing sound.
RxD (Received data): The RxD pin is the Data Receive pin. This is the pin where the receiver receives data.
TxD (Transmitted data): The TxD pin is the Data Transmit pin. This is the pin through which data is transmitted to the receiver.
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