Although the tiltle of the lab is self explanatory, Serial communication has become the standard for inter-computer communication. In contrast to parallel communication in which a number of bytes are transmitted and received simultaneously, serial communication is the form of communication in which the data is transmitted and received as a timed sequence of bits on a single wire. This communication has become the standard for intercomputer communication. In this lab, we've tried to build a serial link between the 8051 microcontroller and Personal Computer using RS-232. Apart from basic communication methodologies some additional features were embedded to assure the secure and reliable communication.
The RS-232 was created for one purpose, to interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) employing serial binary data interchange. So as stated the DTE is the terminal or computer and the DCE is the modem or other communications device. In our case the DTE’s are the computer and the microcontroller and the DCE’s are the COM port at computer and the serial port at microcontroller.
The system, that we developed is a prototype full duplex serial communication system, therefore we programmed it to send data from computer written in a file to microcontroller and send the same data back to computer from microcontroller. To ensure security, we exercised to send and received data in encrypted form to avoid leakage of information, in case the communication medium is tapped. For reliability, a protocol was developed that ensures that data is reached to its destination in its original form and there is no loss of information.
The main objective of this lab was to establish a defendable full duplex serial communication link between the computer and the microcontroller
Serial Communication RS-232
The concept behind serial communications is as follows, data is transferred from sender to receiver one bit at a time through a single line or circuit. The serial port takes 8, 16 or 32 parallel bits from your computer bus and converts it as an 8, 16 or 32 bit serial stream. The name serial communications comes from this fact; each bit of information is transferred in series from one location to another.
In theory a serial link would only need two wires, a signal line and a ground, to move the serial signal from one location to another. But in practice this doesn't really work for a long time, some bits might get lost in the signal and thus altering the ending result. If one bit is missing at the receiving end, all succeeding bits are shifted resulting in incorrect data when converted back to a parallel signal. So to establish reliable serial communications you must overcome these bit errors that can emerge in many different forms.
There are two basic types of serial communications, synchronous and asynchronous. With synchronous communications, the two devices initially synchronize themselves to each other, and then continually send characters to stay in sync. Synchronous communications allows faster data transfer rates than asynchronous methods, because additional bits to mark the beginning and end of each data byte are not required. The serial ports on IBM-style PCs are asynchronous devices and therefore only support asynchronous serial communications.
Asynchronous means "no synchronization", however, the beginning and end of each byte of data must be identified by start and stop bits. The start bit indicates when the data byte is about to begin and the stop bit signals when it ends. The requirement to send these additional two bits causes asynchronous communication to be slightly slower than synchronous.
An asynchronous line that is idle is identified with a value of 1. By using this value to indicate that no data is currently being sent, the devices are able to distinguish between an idle state and a disconnected line. When a character is about to be transmitted, a start bit is sent. A start bit has a value of 0. Thus, when the line switches from a value of 1 to a value of 0, the receiver is alerted that a data character is about to be sent.
RS-232 is a standard developed for homogenizing serial communications between different devices. Many signals are defined in this standard and most of them are not used in our experiment. Only three signals RxD, TxD and GND are used. So, we skip the details of other signals defined in RS-232 standard.
• TxD Serial data is sent on this line from transmitter to receiver. The transmitter holds this line at logic 1 when no data is being transmitted. scanner project, microcontroller,Fluid-Level Detector CD4093B
• RxD The receiver receives data on this line. RxD of receiver is connected to TxD of transmitter so that the receiver receives the data transmitted by the transmitter.
• GND GND signal is the reference signal which must be same for both the transmitter and receiver. It enables them to correctly identify the bits.scanner project, microcontroller
The logic levels defined by RS-232 standard are not compatible with TTL logic levels. TTL logic levels are +5V for logic 1 and 0V for logic 0. But, in RS-232 standard logic 1 level may vary from –3V to –25V and logic 0 level may vary from 3V to 25V. These voltage levels provide protection against noise signals and thus make communication possible over larger distances between the transmitter and receiver. scanner project, microcontroller,RS232 data acquisition,PC based data acquisition vb6 serial data logger software stepper motor control vb6 intel core 2 microprocessor circuit diagram 8048 microcontroller architecture diagram microcontroller to rs232
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