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Serial Communication
As with hardware communication, we 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 speed of transmission and is adjusted according to the needs of the transmission. For the transmission speed of 9600 baud, T is 104 uS.
Pin designations on RS232 connector In order to connect a microcontroller to a
serial port on a PC computer, we 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.
Connecting a microcontroller to a PC via a MAX232 line interface chip.
Using the macro:
At the beginning of the main program, we
need to declare variables RS_TEMP1, RE_TEMP2, TXD, RXD and TX pin on
microcontroller. After resetting a microcontroller the program sends a
greeting message to PC computer: $ PIV16F84 on line $, and is ready
to receive data from RX line.
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