Lecture_03 - Serial Communication

Lecture_03 - Serial Communication - SEE215 Lecture 3 Serial...

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Faculty of Science and Technology Lecture 3 Serial Communication using USART & PC COM ports SEE215
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Parallel communication In theyy last In the last two lectures we have seen examples of parallel data communication. Eight switches were read simultaneously in parallel and eight LED's were written to simultaneously. It is obvious that that 8 wires ( pus a common ground) were used to transfer data from the switches to PINC and from PORTA to the LEDS.
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In fact, the data transfer within the AVR ATMega128 is also done on a 8 bit wide data bus. Hence it is an 8 bit processor 8 bit internal data bus Internal data bus
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8 bit external data busses
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Serial communication In theyy last It is obvious that if we wish to communicate 8 bit wide data over long distances, we must have very long and thick (8 +1 wires) transmission lines. This is often difficult to implement and certainly expensive An alternative to sending 8 bits of data simultaneously is to send the 8 bits serially, IE. One after the other. This requires only two wires, one for the serial data signal and one for for the return path. (Three wires if data is to be transferred in two directions)
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Asynchronous format Element length = 1/baudrate Stop bit may be one or two elements. Parity may be NONE (absent) , ODD or EVEN
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Serial communication & ATMega128 In theyy last The data transfer data to and from the ATMega128 a serial data transfer occurs between it and the host PC's COM port. The data on this data bus has gone through some voltage translation, to improve noise immunity and reliability. This is known as RS232 ( R ecommended S tandard 232 for data transfer) A data 0 will be a voltage between +3 to +15 Volt & a data 1 will be a voltage between -3 to -15 Volt
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Asynchronous – RS232
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Level translator to convert TTL levels from USART to RS232 levels ( see circuit diagram) RS232 PORT 0 (USART0)
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Serial PORTS & PC’S Generally notebook computers do not have COM ports. You will need a USB-COM converter to be able to communicate with RS-232
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Serial communication & USART In theyy last The conversion from parallel data to serial (and vica versa) occurs in the special I/O peripheral the -U S A R T
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The USART In theyy last The USART is the Universal Synchronous and Asynchronous serial Receiver and Transmitter .
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This note was uploaded on 09/27/2009 for the course SEB 323 - S taught by Professor Professor during the Three '09 term at Deakin.

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Lecture_03 - Serial Communication - SEE215 Lecture 3 Serial...

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