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Interfaces and Synchronization

Interfaces and Synchronization. Martin Weiss. EIA 232D Interface Standard. Synonymous with ITU V.24 Asynchronous interface Up to 19.2kbps 50 foot maximum distance between DCE and DTE. Other Interface Standards. EIA 449 - Uses EIA-422 (balanced) or EIA-423 (unbalanced) signalling standards

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Interfaces and Synchronization

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  1. Interfaces and Synchronization Martin Weiss

  2. EIA 232D Interface Standard • Synonymous with ITU V.24 • Asynchronous interface • Up to 19.2kbps • 50 foot maximum distance between DCE and DTE

  3. Other Interface Standards • EIA 449 - Uses EIA-422 (balanced) or EIA-423 (unbalanced) signalling standards • EIA 530 - Same as EIA 449 except with a 25 pin connector

  4. Signalling Standards Circuit Type Max. Separation (m) Max. Bit Rate EIA-423 10 100 1000 100kbps 10kbps 1kbps EIA-422 10 100 1000 10Mbps 1Mbps 100kbps

  5. Main EIA 232D Signals • Receive data (RxD) - Pin 2 • Transmit data (TxD) - Pin 3 • Request to Send (RTS) - Pin 4 • Clear to Send (CTS) - Pin 5

  6. Main EIA 232D Signals • Data Set Ready (DSR) - Pin 6 • Data Terminal Ready (DTR) - Pin 20 • Ring Indicator (RI) - Pin 22 • Carrier Detect (CD) - Pin 8

  7. Modem Modem DTR DTR DSR RTS CTS DSR Data TxD DCD RxD EIA 232D Protocol

  8. Questions • For data transfer, when would we want to transfer bits one at a time, and when as a group? • Why do we have to worry about synchronization? • How can we begin to quantify performance issues?

  9. Bit Synchronization • The receiver must know when a bit starts and when it stops • Normally, synchronization sequences are necessary

  10. Character Synchronization • When does a character start?

  11. Asynchronous Communications • Characters are transmitted when they are generated • The receiver must be configured so that the gross transmission characteristics are identical to the transmitter

  12. Implementation of Async • Line is normally in a logical “High” state • Preceding a character is a “Start Bit” (Low for one bit time) • Subsequent bits may be low or high • Character may be ended by stop bit(s)

  13. Implementation of Async Start 0 0 1 1 0 1 0 Stop Stop Parity =?

  14. Discussion of Async • Very simple to implement • Inefficient • Alternative: synchronous transmission

  15. Discussion of Async

  16. Synchronous Transmission • Transmitter and receiver are synchronized at the bit and character level prior to transmission • Messages may still arrive asynchronously • Synchronous systems are normally more complex

  17. Propagation time a = Transmission time Performance Analysis of Communications Links • Consider the effect of propagation delay and transmission rate Recall that

  18. Definitions • Let U = (throughput)/(capacity) = T/R • Throughput is the number of bits actually transmitted per unit time • Capacity is the number of bits that could be transmitted per unit time • R = data rate of the channel • d = maximum distance between any two stations

  19. frame length = transmission time + propagation delay Definitions • V = velocity of signal propagation • L = frame length (average or fixed) • T = throughput • Assuming no overhead, Number of bits T = Time from source to destination

  20. Illustration (a < 1) t0 Start of Transmission t0+a Start of Reception t0+1 End of Transmission t0+1+a End of Reception

  21. Illustration (a > 1) t0 Start of Transmission t0+1 End of Transmission t0+a Start of Reception t0+1+a End of Reception

  22. frame length T = Propagation delay + transmission time Utilization of a Baseband Bus Utilization = Throughput/Capacity

  23. U vs. a U 1.0 0.8 0.6 0.4 0.2 a 1 5 10 15 20

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