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Serial Communication Interface (SCI)

Serial Communication Interface (SCI). Ellenor Brown Howard Liles Algan Samur. Presentation Outline. Howard Liles. Ellenor Brown. Algan Samur. Types of data transmission Parallel Serial Serial Communication Synchronous Asynchronous Baud and Bit Rates

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Serial Communication Interface (SCI)

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  1. Serial Communication Interface (SCI) Ellenor Brown Howard Liles AlganSamur

  2. Presentation Outline Howard Liles Ellenor Brown AlganSamur • Types of data transmission • Parallel • Serial • Serial Communication • Synchronous • Asynchronous • Baud and Bit Rates • Asynchronous Serial Transmission • Start Bit • Data Bit • Stop Bit • Parity Bit • Noise • SCI Registers • Show two examples of how data words are transmitted

  3. Data Transmission Power supply circuit Electronic devices communicating with each other Desktop computer Lights Turbine generators Printer Hard drive

  4. Types of Data Transmission • Parallel Data Transmission • One word (N bits) at a time Receiver (Monitor) Receiver (printer) = bits Word Transmitter (CPU) Transmitter (microprocessor) Serial Data Transmission One bit at a time

  5. Parallel vs. Serial • Parallel requires more transfer lines • Bits have to be synchronized • Fast, but expensive • Examples: • Printer cables • Serial requires less transfer lines • Transfers one bit at a time • Slow comparatively, but less expensive • Examples: • USB, Firewire, ethernet

  6. Serial Communication • Synchronous Serial Communication • Transmitter and Receiver have synchronized clocks • Data must be sent constantly in order for them to stay synchronized • Any data not sent on a regular clock cycle is considered noise • Transmission parameters are set up before sending data • 30% faster than asynchronous transmission for large continuous blocks of data • Clock rate determines data transfer rate Receiver Asynchronous Communication Transmitter and receiver do not have synchronized clocks and act independently Simpler and less expensive than synchronous Start, Stop and Parity “caution” bits are sent with each word of data Transmitter Transmitter Receiver Word

  7. Comparisons Andrew Byrley

  8. Baud and Bit Rates • Baud Rate (Bd) is the rate at which Symbols are transferred. A symbol is a given signaling event ‘Symbols/second’ • Number of bits per Symbol is Hardware Specific (our hardware uses 1 baud/bit) Conversion factor: 1 bit = 1 Symbol = 1 baud • Bit rate (bps) - the rate at which bits are transmitted or “bits/second” Conversion Equation: Bit rate (bps) = baud rate × number of bits per baud

  9. Baud and Bit Rates Cont.’d • Some bits are data and some are not! • Remember the start, stop, and parity bits which are also known as “overhead bits” • Data throughput can be determined by Characters per second (cps) Cps = actual rate of data being sent 1 Standard Character = 1 Bit • Characters per second (cps)=Bit rate*(character bits/total bits) • *Remember CPS is not same as bytes/second. CPS does not include overhead!

  10. Baud and Bit Rates Example Example 1: You have an asynchronous serial connection. Assuming 2 bits per symbol, 9600 bd line speed, 8 bit data format with no parity, 1 start bit and 1 stop bit, calculate the throughput in cps. Bit rate (bps) = baud rate × number of bits per baud bps= 9600x2=19200 (cps)=Bit rate*(character bits/total bits) cps=19200*(8/10)= 15360

  11. Presentation Outline Howard Liles Ellenor Brown AlganSamur • Types of data transmission • Parallel • Serial • Serial Communication • Synchronous • Asynchronous • Baud and Bit Rates • Asynchronous Serial Transmission • Start Bit • Data Bit • Stop Bit • Parity Bit • Noise • SCI Registers • Show two examples of how data words are transmitted

  12. Asynchronous Serial Communication Data Stop Receiver Transmitter Parity Start Transmitter and Receiver are independent Transmitter sends ‘Start’, ‘Parity’ and ‘Stop’ bits with each word of data Data received between a Stop bit and the next Start bit is ignored

  13. Data Frame Format Data Stop Receiver Transmitter Parity Start Start bit – Indicates beginning of data Data bit – Data being transmitted Parity bit – Integrity check Stop bit – Indicates end of data word Data frame size: 10 or 11 bits

  14. Start Bit • One bit • Indicates the beginning of word • Opposite polarity from idle bit state • Idle state for HCS12 is 1’s • Start bit = 0

  15. Data Bits • Actual data being transmitted plus a parity bit • Most common mode: • 8-bit transmission • Used for ASCII character transmission (7-bit ASCII + 1-bit parity = 8-bit) • Less common mode: • 9-bit transmission • Can be used to send a full byte of data + parity bit • HCS12 sends least significant bit (LSB) first

  16. Parity Bit • Used to determine if an error occurred during data transmission • Error Detection • Transmitter calculates proper parity bit • Receiver calculates parity bit based on data it received • Receiver compares its parity bit to the one it received Evan Johnson

  17. Parity Bit • 2 types of Parity functionality • Even Parity • Parity bit is set to 1 if there is an odd number of 1’s in data bits  # of 1’s becomes even • Odd Parity • Parity bit is set to 1 if there is an even number of 1s in data bits  # of 1’s becomes odd) • Even/Odd Parity is set by user on HCS12 Evan Johnson

  18. Stop Bit • 1 or 2 bits • Used due to asynchronous nature • Directly after the parity bit • Stop bit is the same as the polarity of the data-line’s idle state • Idle state for HCS12 = all 1’s • Stop bits = 1

  19. Asynchronous Data Transmission LSB Data Bit 0 Data Bit 5 Start Bit Data Bit 1 Parity Bit Stop Bit Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 6 Data Bit 7 0 1 1 0 0 1 0 1 0 0 1 • Example 1: • Hex# 4A16 is to be sent with one start bit, evenparity, 8-bit data length and one stopbit • 4A16 = 0100 10102

  20. Asynchronous Data Transmission Data Bit 1 Data Bit 6 Data Bit 5 Start Bit Parity Bit Stop Bit Data Bit 0 Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 7 0 0 0 1 0 0 1 0 1 1 1 • Example 2: • Hex# B416 is to be sent with one start bit, evenparity, 8-bit data length and one stop bit • B416 = 1011 01002

  21. Asynchronous Data Transmission Start Bit Data Bit 0 Data Bit 1 Parity Bit Stop Bit Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7 1 1 1 0 0 0 1 0 1 1 0 • Example 3: • Hex# B416 is to be sent with one start bit, oddparity, 8-bit data length and one stop bit • B416 = 1011 01002

  22. Error sources • Frame shift • Detected when a logic 0 is accepted as the stop bit • Overrun • Software fails to read the SCI data register before the shift register receives the next frame • Noise • SCI detects noise on the receiver input

  23. Framing Error • Occurs when stop bit is not where receiver expects it to be • Detected when a logic 0 is accepted as the stop bit • Ex: “4” bit is skipped and stop bit is one bit before it should be 1 2 3 4 5 6 7

  24. Overrun RECEIVER SOFTWARE REGISTER TRANSMITTER Software fails to read the SCI data register before it receives the next frame Data in the shift register is lost Data already in the SCI data registers is not affected

  25. Noise Detection • SCI detects noise on the receiver input

  26. Presentation Outline Howard Liles Ellenor Brown AlganSamur • Types of data transmission • Parallel • Serial • Serial Communication • Synchronous • Asynchronous • Baud and Bit Rates • Asynchronous Serial Transmission • Start Bit • Data Bit • Stop Bit • Parity Bit • Noise • SCI Registers • Coding example

  27. SCI Baud Rate Registers SCIBDH & SCHBDL - $00C8-$00C9 • 13-Bits register determines SCI Baud rate • Baud rate generator is disabled until TE or RE bit is set for the first time after reset. • Baud rate generator is turned off when this register contains $0000 • Note: Writing to SCIBDH has no effect w/out writing to SCIBDL

  28. Implementation Specific Features (S12SCIV2) • 13-bit baud rate selection • 8- or 9-bit data format • Separately enabled transmitter and receiver • Programmable transmitter output parity • Interrupt driven operation with 8 flags • 8 registers used to control SCI ($00C8-$00CF) • Uses Port S pins 0 & 1 for RXD and TXD respectively

  29. SCI Control Register 1SCICR1 - $00CA • M (data format mode) - 0: 8 data bits, • 1: 9 data bits. • Both use 1 start bit and 1 stop bit • PE (parity enable) – 0: Off, 1: On • PT (parity type) – 0: Even, 1: Odd

  30. SCI Control Register 2SCICR2 - $00CB • TIE (transmit interrupt enable) – 0: disables interrupts for transmit data register empty, 1: enables • TCIE (transmit complete interrupt enable) – 0: disables interrupts for transmit complete, 1: enables • RIE (receiver interrupt enable) – 0: disables interrupts for receiver full and overrun , 1: enables • ILIE (idle line interrupt enable) – 0: disables interrupts for idle line, 1: enables • TE (transmit enable) – 0: disable transmitter, 1: enable • RE (receiver enable) – 0: disable receiver, 1: enable

  31. SCI Status Register 1SCISR1 - $00CC • Read only register • Can be used to provide input to the microcontroller for generation of SCI interrupts • TDRE (transmit data register empty) – 0: No byte transferred,1: byte successfully transferred to transmit shift register • TC (transmit complete flag) – 0: transmission in progress, 1: no transmission in progress • RDRF (receive data register full) – 0: no data in data register, 1: data in data register • IDLE (idle flag) – 0: receiver input is active, 1: receiver input has become idle

  32. SCI Status Register 1SCISR1 - $00CC • OR (overrun)– 0: no overrun, 1: overrun (overrun happens when new data is received before old data is read) • NF (noise flag) – 0: disable, 1: enable • FE (framing error flag)– 0: disable, 1: enable • PF (parity error)– 0: No parity error, 1: parity error

  33. SCI Status Register 2SCISR2 - $00CD • BK13 (break transmit character length) – 0: 10 or 11 bit, 1: 13 or 14 bit • TXDIR (transmitter pin direction) – 0: TXD pin used as input, 1: TXD pin used as output. (used only in single wire mode) • RAF (receiver active flag) – 0: no reception in progress, 1: reception in progress

  34. SCI Data RegistersSCIDRH &SCIDRL - $00CE - $00CF • SCIRDL contains incoming bytes of data from serial port • R8 – bit 8 of received 9-bit data • T8 – bit 8 of transmitted 9-bit data

  35. SCI is easy • SCI module makes it easy to send/receive data • SCI module encodes data into standard NRZ format! • Hardest part is setting up baud rate • Can use either polling or interrupt based logic to drive SCI • SCIDRH/SCIDRL are like two registers in one. • Read this register to receive data • Write to this register to send data

  36. Example • First, calculate baud rate. Assume 8MHz bus and desired baud rate is 9600 • SCI module runs at bus speed • Desired value for SCIBR is 52 • You will have some error margin • Exact solution is 52.0833 • Actual baud rate is 9615.3 (0.160% error)

  37. Example • Write SCIBR ($0034) to SCIBDH/SCIBDL • For 8-bit, no parity, no interrupts, default values will work • Simply enable transmit and receive in SCICR2 • Read from SCIDRL to receive 8-bit data • Write data to SCIDRL to send 8-bit data

  38. Code Example

  39. Code Example

  40. #include <hidef.h> /* common defines and macros */ #include <mc9s12c32.h> /* derivative information */ #pragma LINK_INFO DERIVATIVE "mc9s12c32" void SCI_init(void){ int BR = 0x0034; SCIBDH = BR>>8; //stores high Byte SCIBDL = BR; //stores low Byte SCICR2 = 0x0C; //sets TE and RE to 1 } char SCI_getByte(void){ while (!(SCISR1_RDRF)) ;//waits FOREVER until receive register is full return SCIDRL; } void SCI_sendByte(char data){ while (!(SCISR1_TDRE)) ;//waits FOREVER until transmit register is empty SCIDRL = data; //return void; } void main(void) { //variable declarations must go at beginning /* put your own code here */ EnableInterrupts; //required code as per instructions MISC = 0x03; PEAR = 0x0C; MODE = 0xE2; //Call function to setup SCI SCI_init(); //Main loop while(1) { char data = SCI_getByte(); SCI_sendByte(data); } /* loop forever */ /* please make sure that you never leave this function */ }

  41. Thank You! Any Questions?

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