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lecture_note9 - CpE 390: Microprocessor Systems Lecture 9...

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Stevens Institute of Technology 1 CpE 390: Microprocessor Systems Lecture 9 68HC12 Serial Interface – SCI
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Stevens Institute of Technology 2 Why Serial Communication? - Parallel data transfer requires many I/O pins. - Many I/O devices do not have high data rate to justify the use of parallel data transfer. - Data synchronization for parallel transfer is difficult to achieve over a long distance. - Cost consideration What is SCI? - A interface designed to transfer data only in asynchronous mode that utilizes the EIA-232 standard. What is SPI? - A protocol proposed by Motorola to facilitate the data exchange between the microcontrollers designed by Motorola and peripheral devices.
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Stevens Institute of Technology 3 Asynchronous Serial Data Communication - Often used for data communication between a DTE (data termination equipment) and a DCE (data communication equipment) with or without a modem. DTE DCE Computer or terminal Modem Communication link Figure 9.0 A data communication system - there are two kinds of data communication links: 1. simplex link: only communicate in one direction 2. half-duplex link: two-direction link, only one direction at a time 3. full-duplex link: communicate in both directions simultaneously
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Stevens Institute of Technology 4 Types of communication link configuration (a) Point-to-point Station Master Slave 1 Slave 2 Slave n ...... (b) Multi-drop Figure 9P.2 Point-to-point and multi-drop communication links The RS232 Standard -was the most widely used physical level interface for data communication -specifies 25 interchange circuits for DTE/DCE use -was established in 1960 by Electronics Industry Association (EIA)
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Stevens Institute of Technology 5 EIA-232-E Mechanical Specification - Specifies a 25-pin connector - Specifies exact dimensions of each pin. Signal Name Protective ground Transmitted data Received data Request to send Clear to send Data set ready Signal ground Carrier detect Reserved Secondary carrier detect Secondary clear to send Secondary transmitted data Transmit clock Secondary received data Receiver clock Unassigned Secondary request to send Data terminal ready Signal quality detect Ring indicator Data rate select Signal Direction Both to DCE to DTE Figure 9.1 EIA-232-E connector and pin assignment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
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Stevens Institute of Technology 6 EIA-232-E Procedural Specification - Define the sequence of events that occurs during data transmission Case 1 . Two DTEs connected via a point-to-point link using a modem. Tx Rx DCD CTS DSR GND RTS Computer (DTE) Modem (DCE) Direct link Tx: transmit data CTS: clear to send Rx: receive data RTS: request to send DCD: data carrier detect DSR: data set ready Figure 9.2 Point-to-point asynchronous connection
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Stevens Institute of Technology 7 Sequence of events occurred during data transmission over dedicated link Local Remote 1. DCE asserts DSR 2. DTE asserts RTS 3. DCE asserts CTS 4. DTE starts to send data (to local DCE) 5. DCE sends out a carrier and then the modulated data 6. DCE asserts DCD 7. DTE waits for arrival of data 8. DCE sends out demodulated received data 9. DEC receives demodulated data Ti me
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lecture_note9 - CpE 390: Microprocessor Systems Lecture 9...

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