RS 232 SERIAL COMMUNICATION

SCI is an abbreviation for Serial Communication Interface and, as a special subsystem of microcontroller PIC16F877A. It provides RS232 serial communication with PC easily. As with hardware communication, use standard NRZ (Non Return to Zero) format also known as 8 (9)-N-1, or 8 or 9 data bits, without parity bit and with one stop bit. Free line is defined as the status of logic one. Start of transmission - Start Bit, has the status of logic zero. The data bits follow the start bit (the first bit is the low significant bit), and after the bits we place the Stop Bit of logic one. The duration of the stop bit 'T' depends on the transmission rate and is adjusted according to the needs of the transmission. For the transmission speed of 9600 baud, T is 104μs.

In order to connect a microcontroller to a serial port on a computer, need to adjust the level of the signals so communicating can take place. The signal level on a PC is -10V for logic zero, and +10V for logic one. Since the signal level on the microcontroller is +5V for logic one and 0V for logic zero, we need an intermediary stage that will convert the levels. One chip specially designed for this task is MAX232. This chip receives signals from -10 to +10V and converts them into 0 and 5V. The circuit for this interface is shown in the.