However many microcontrollers give a 0 to 5V output and require an intermediate buffer circuit to convert the 0 to 5 volts to +10 and -10V required by the RS232 port. Few Microcontrollers have built-in serial ports that allow for direct connection with the RS232 serial port of the PC. It accepts the standard digital logic values of 0 & 5 volts and converts them to the RS232 standard of +10 & -10 volts. Max 232 acts as a buffer driver for the processor. Interfacing RS232 to Microcontrollers using Max 232 Max 232 – The Level Shifter IC for PC Interface Most devices that use RS-232 cable are CPS and laptops. Both activities are stable and the system goes to sleep mode or shutdown mode. The first auto-shutdown pulse monitors both receiver and transmitter activity. The Max 232 device is used to communicate with the DTE and DCE devices through RS-232 cable. Pin 2 and Pin 3 are used for transmitting and receiving the data. It means that whenever a transceiver is connected to the RS-232 port but it is not sending data. The auto-shutdown pulse will shut itself down whenever there is not any activity on the signal for 30sec. The system will shut down whenever the RS-232 device is not used. The RS-232 is placed to work in the low power shutdown mode. The Auto-shutdown feature is intended to save power. PIN 23: Data Signal Rate Detector Application of RS232 All the modems designed for directly connected to the phone network equipped with the auto-answer. PIN 22: (Ring Indicator): The ringing indicator means the DCE informs the DTE that the phone is ringing. PIN 21: (Signal Quality Detector) This pin Indicates the quality of the received carrier signal because the transmitting modem must be sent 0 or either 1 at each bit time, the modem controls the timing of the bits from the DTE. PIN 15, 17, 24 Synchronous modems use the signals on these pins. Normally this signal is used by DCE auto-answer mode. PIN9: This pin is a DTE serial connector, this signal follows the incoming ring to an extent. This signal is activated when a suitable carrier is established between the local and remote DCE devices. PIN 8: This pin is also known as received line signal detector carrier detect. The DCE and DTE work properly across the serial interface and the pin-7 must be connected both ends without interface would not work. PIN 7: This pin is the common reference for all signals, including data, timing, and control signals. Normally terminals cannot transmit the data until clear to send transmission is received from the DCE. PIN 4, PIN 5, PIN 6, PIN 20: These pins are the handshaking pins(flow of control).
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