serial port
Serial Port The microcontroller AT89C51 has an inbuilt UART for carrying out serial communication. The serial communication is done in the asynchronous mode. A serial port, like other PC ports, is a physical interface to establish data transfer between computer and an external hardware or device. This transfer, through serial port, takes place bit by bit.
IBM introduced the DB-9 RS-232 version of serial I/O standard, which is most widely used in PCs and several devices. In RS232, high and low bits are represented by flowing voltage ranges: Bit
Voltage Range (in V)
0
+3
+25
1
-25
-3 The range -3V to +3V is undefined. The TTL standards came a long time after the RS232 standard was set. Due to this reason RS232 voltage levels are not compatible with TTL logic. Therefore, while connecting an RS232 to microcontroller system, a voltage converter is required. This converter converts the microcontroller output level to the RS232 voltage levels, and vice versa. IC MAX232, also known as line driver, is very commonly used for this purpose. The simplest connection between a PC and microcontroller requires a minimum of three pins, RxD (receiver, pin2), TxD (transmitter, pin3) and ground (pin5) of the serial port of computer.
TxD pin of serial port connects to RxD pin of controller via MAX232. And similarly, RxD pin of serial port connects to the TxD pin of controller through MAX232. MAX232 has two sets of line drivers for transferring and receiving data. The line drivers used for transmission are called T1 and T2, where as the line drivers for receiver are designated as R1 and R2. The connection of MAX232 with computer and the controller is shown in the circuit diagram.
An important parameter considered while interfacing serial port is the Baud rate which is the speed at which data is transmitted serially. It is defined as number of bits transmitted or received per second. It is generally expressed in bps (bits per second).
IBM introduced the DB-9 RS-232 version of serial I/O standard, which is most widely used in PCs and several devices. In RS232, high and low bits are represented by flowing voltage ranges: Bit
Voltage Range (in V)
0
+3
+25
1
-25
-3 The range -3V to +3V is undefined. The TTL standards came a long time after the RS232 standard was set. Due to this reason RS232 voltage levels are not compatible with TTL logic. Therefore, while connecting an RS232 to microcontroller system, a voltage converter is required. This converter converts the microcontroller output level to the RS232 voltage levels, and vice versa. IC MAX232, also known as line driver, is very commonly used for this purpose. The simplest connection between a PC and microcontroller requires a minimum of three pins, RxD (receiver, pin2), TxD (transmitter, pin3) and ground (pin5) of the serial port of computer.
TxD pin of serial port connects to RxD pin of controller via MAX232. And similarly, RxD pin of serial port connects to the TxD pin of controller through MAX232. MAX232 has two sets of line drivers for transferring and receiving data. The line drivers used for transmission are called T1 and T2, where as the line drivers for receiver are designated as R1 and R2. The connection of MAX232 with computer and the controller is shown in the circuit diagram.
An important parameter considered while interfacing serial port is the Baud rate which is the speed at which data is transmitted serially. It is defined as number of bits transmitted or received per second. It is generally expressed in bps (bits per second).