1 / 39

Serial Communication Interface (SCI)

Serial Communication Interface (SCI). Presented by: Lakmal Kaviratna Thomas Herrmann Nicolaas Ostendorf 13 November 2012. Lakmal Kaviratna. Data Transmission Types. Transmitting Data b 1 b 2 b 3 b 4 b 5 b 6 b 7 b 8. -- Bit i. i. Transmitting Data b 1 b 2 b 3 b 4 b 5 b 6 b 7 b 8. 1.

sheng
Download Presentation

Serial Communication Interface (SCI)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Serial Communication Interface(SCI) Presented by: LakmalKaviratna Thomas Herrmann NicolaasOstendorf 13 November 2012

  2. LakmalKaviratna Data Transmission Types Transmitting Data b1b2b3b4b5b6b7b8 -- Bit i i Transmitting Data b1b2b3b4b5b6b7b8 1 2 3 4 Serial 1 2 5 3 4 6 7 8 5 Parallel 6 7 Received Data b1b2b3b4b5b6b7b8 8 Received Data b1b2b3b4b5b6b7b8

  3. LakmalKaviratna Parallel vs Serial Data Transmission

  4. LakmalKaviratna Types of 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 -- Bit of Data Receiver Transmitter Δt

  5. LakmalKaviratna Types of Serial Communication • 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 -- Start Bit -- Parity Bit -- Stop Bit -- Bit of Data Transmitter Transmitter

  6. LakmalKaviratna Synchronous vs Asynchronous Serial Communication

  7. LakmalKaviratna Baud and Bit Rates • Symbol – a pulse representing an integer number of bits • Baud (Bd) – Rate which Symbols are transferred. (Symbols/second) • The number of bits per Symbol is Hardware Specific • Bit rate (bps) – Rate which bits are transmitted. (bits/second) • Data Throughput (dtp) – Rate which bits of DATA are transmitted. (Characters/second) • Remember: in asynchronous transfer, not all bits are data (start/stop/parity bits are also present)

  8. LakmalKaviratna Example Baud and Bit Rates • Example: 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.

  9. Thomas Herrmann Asynchronous Serial Communication • Transmitter and Receiver operate independently of each other • Transmitter must send a Start, Parity, and Stop bit with each package or ‘word’ of Data • Any signal after a Stop bit and before a Start bit is ignored

  10. Thomas Herrmann Data Signal Format • Idle State – signal between data • Start Bit – signifies start of data transmission • Data Packet – data being transmitted • Parity Bit – fidelity check of data for receiver • Stop Bit – signifies end of data transmission • Data – 10-11 bits

  11. Thomas Herrmann Idle State • Idle signal is a uniform stream of bits at the idle polarity state • For the HCS12, the idle state is 1

  12. Thomas Herrmann Start Bit • A single bit is used to indicate the start of the transmission of a single word or packet • The polarity of the start bit is opposite the polarity of the idle bits • For the HCS12, the start bit is 0

  13. Thomas Herrmann Data Bits • Actual data that is being transmitted • 8-bit mode transmission, typical • 7 bits of data and 1 parity bit (Used for ASCII) • 9-bit mode transmission, less common • 8 bits of data and 1 parity bit (Full byte transmission) • The HCS12 requires the least significant bit first

  14. Thomas Herrmann Parity Bit • Last bit in data packet used to determine the fidelity of the received signal and check for errors in a transmission • Transmitter calculates parity bit based on data sent • Receiver estimated parity bit with the data received • Receiver compares received parity and estimate parity

  15. Thomas Herrmann Parity Bit • Two types of parity functionality • Even Parity • The parity bit is set to 1 if the total number of 1s in the data bits is odd, total number of 1s becomes even • Odd Parity • The parity bit is set to 1 if the total number of 1s in the data bits is even, total number of 1s becomes odd • Even/Odd Parity for the HCS12 set by User

  16. Thomas Herrmann Stop Bit • Signifies end of packet – necessary for asynchronous transmission • Can be 1-2 bits • Stop bit polarity is the same as the idle state polarity • For the HCS12, stop bit is 1

  17. Thomas Herrmann Example 1 Construct the asynchronous signal for the transmission of 7516 for the HCS12 with8-bit mode, even parity, and one stop bit 7516 = 0111 01012 10

  18. Thomas Herrmann Example 2 Construct the asynchronous signal for the transmission of 5A16 for the HCS12 with8-bit mode, even parity, and one stop bit 5A16 = 0101 10102 10

  19. Thomas Herrmann Example 3 Construct the asynchronous signal for the transmission of B916 for the HCS12 with 9-bit mode, odd parity, and one stop bit B916 = 1011 10012 10

  20. Thomas Herrmann Types of Error • Receiver Overrun • Noise Error • Frame Error • Parity Error

  21. Thomas Herrmann Receiver Overrun • Software fails to process 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

  22. Thomas Herrmann Noise Error • Signal noise can cause the receiver to incorrectly read a start bit or false data • This can be compensated by sampling at a higher frequency that the incoming signal • Multiple reading can be taken of each transmitted bit • These readings are averaged to determine the intended transmission

  23. Thomas Herrmann Frame 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: The fourthbit is skipped and stop bit is one bit before it should be 1 2 3 4 5 6 7

  24. Parity Error • The transmitter determines and send the correct parity bit • The receiver determines what the parity bit should be based on the signal received • If the transmitter and receiver parity bits do not match, then there is a known error • This does not account for an even number of errors in the data bits

  25. NicolaasOstendorf SCI Distinctive Features (S12SCIV2) • Full duplex operation • 13-bit baud rate selection • Programmable 8-bit or 9-bit data format • Separately enabled transmitter and receiver • Programmable transmitter output parity • Two receiver wake up methods • 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 • SCI is summarized on pages 383-393 in MC9S12C Family Reference Manual

  26. NicolaasOstendorf SCI Baud Rate Registers:SCIBDH & SCHBDL - $00C8-$00C9 • 13-bit register determines SCI baud rate • Baud rate generator is disabled until TE or RE bit is set for the first time after reset • Writing to SCIBDH has no effect without writing to SCIBDL

  27. NicolaasOstendorf SCI Control Register 1:SCICR1 - $00CA • Data Format Bit (M) – 0: 8-bit, 1: 9-bit • Both 8-bit and 9-bit data formats have 1 start bit and 1 stop bit • Parity Enable Bit (PE) – 0: Disabled, 1: Enabled • Parity Type Bit (PT) – 0: Even, 1: Odd

  28. NicolaasOstendorf SCI Control Register 2:SCICR2 - $00CB • Transmit Interrupt Enable (TIE) – 0: Disables interrupts for transmit data register empty flag, 1: Enables • Transmit Complete Interrupt Enable (TCIE) – 0: Disables interrupts for transmit complete flag, 1: Enables • Receiver Interrupt Enable (RIE) – 0: Disables interrupts for receiver full or overrun flags, 1: Enables • Idle Line Interrupt Enable (ILIE) – 0: Disables interrupts for idle line flag, 1: Enables • Transmit Enable (TE) – 0: Disables transmitter, 1: Enables • Receiver Enable (RE) – 0: Disables receiver, 1: Enables

  29. NicolaasOstendorf SCI Status Register 1:SCISR1 - $00CC • Read only register • Transmit Data Register Empty (TDRE) – 0: No byte transferred to transmit shift register, 1: Byte successfully transferred • Transmit Complete (TC) – 0: Transmission in progress, 1: No transmission in progress • Receive Data Register Full (RDRF) – 0: No data in SCI data register, 1: Data in SCI data register

  30. NicolaasOstendorf SCI Status Register 1:SCISR1 - $00CC • Overrun (OR) – 0: No overrun, 1: Overrun • Noise Flag (NF) – 0: No noise, 1: Noise • Framing Error (FE) – 0: No framing error, 1: Framing Error • Parity Error (PE) – 0: No parity error, 1: Parity error

  31. NicolaasOstendorf SCI Status Register 2:SCISR2 - $00CD • Break Transmit Character Length (BK13) – 0: 10 or 11 bits long, 1: 13 or 14 bits long • Transmitter Pin Direction (TXDIR) – 0: TXD pin used as input, 1: TXD used as output (used only in single wire mode) • Receiver Active Flag (RAF) – 0: No reception in progress, 1: Reception in progress

  32. NicolaasOstendorf SCI Data Registers:SCIRDH & SCIRDL - $00CE-$00CF • SCIRDL contains incoming bytes of data from serial port • R8 – Bit 8 of received data in 9-bit format • T8 – Bit 8 of transmitted data in 9-bit format

  33. NicolaasOstendorf Example • First calculate baud rate: • Assume 8MHz bus and desired baud rate is 9600 • Desired value for SCIBR is 52 • You will have some error margin • Exact solution: 52.0833 • Actual baud rate: 9615.3 (0.160% error)

  34. NicolaasOstendorf Example • Write SCIBR ($34) to SCI Baud Rate Registers (SCIBDH/SCIBDL) • Default values work for 8-bit, no parity, and no interrupts • Enable transmit and receive in SCICR2 • Read from SCIDRL to receive 8-bit data • Write data to SCIDRL to send 8-bit data

  35. NicolaasOstendorf Code Example: Help set up SCI in CodeWarrior #include <hidef.h> /* common defines and macros */ #include <mc9s12c32.h> /* derivative information */ #pragma LINK_INFO DERIVATIVE "mc9s12c32" void SCI_init(void){ int BR = 0x34; SCIBDH = (unsigned char)(BR>>8); //stores high Byte SCIBDL = (unsigned char)(BR); //stores low Byte SCICR2 = 0x0C; //sets TE and RE to 1 } unsigned char SCI_getByte(void){ while (!(SCISR1_RDRF)) ;//waits until receive register is full return SCIDRL; } void SCI_sendByte(unsigned char data){ while (!(SCISR1_TDRE)) ;//waits until transmit register is empty SCIDRL = data; //return void; } void main(void) { //variable declarations must go at beginning EnableInterrupts; MISC = 0x03; PEAR = 0x0C; MODE = 0xE2; //Call function to setup SCI SCI_init(); //Main loop for(;;) { SCI_sendByte(SCI_getByte()); } /* wait */ /* please make sure that you never leave this function */ }

  36. NicolaasOstendorf Code Example #include <hidef.h> /* common defines and macros */ #include <mc9s12c32.h> /* derivative information */ #pragma LINK_INFO DERIVATIVE "mc9s12c32" void SCI_init(void){ int BR = 0x34; SCIBDH = (unsigned char)(BR>>8); //stores high Byte SCIBDL = (unsigned char)(BR); //stores low Byte SCICR2 = 0x0C; //sets TE and RE to 1 } unsigned char SCI_getByte(void){ while (!(SCISR1_RDRF)) ;//waits until receive register is full return SCIDRL; } void SCI_sendByte(unsigned char data){ while (!(SCISR1_TDRE)) ;//waits until transmit register is empty SCIDRL = data; //return void; }

  37. NicolaasOstendorf Code Example void main(void) { //variable declarations must go at beginning EnableInterrupts; MISC = 0x03; PEAR = 0x0C; MODE = 0xE2; //Call function to setup SCI SCI_init(); //Main loop for(;;) { SCI_sendByte(SCI_getByte()); } /* wait */ /* please make sure that you never leave this function */ }

  38. Questions?

  39. References • MC9S12C Family Reference Manual • Past Student Lectures • http://en.wikipedia.org/wiki/Symbol_rate • http://en.wikipedia.org/wiki/Baud

More Related