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ME 4447/6405

Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Instructor: Professor Charles Ume Serial Communication Interface. ME 4447/6405. Types of Data Transmission Parallel Communication Serial Communication Applications Serial Communication Formats

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ME 4447/6405

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  1. Microprocessor Control of Manufacturing Systems and Introduction to Mechatronics Instructor: Professor Charles Ume Serial Communication Interface ME 4447/6405

  2. Types of Data Transmission Parallel Communication Serial Communication Applications Serial Communication Formats Serial Communication with the MC9S12C32 Example Lecture Outline

  3. Importance Most electronic devices must communicate with other devices to either control them or send data to them Standardization The two communicating devices must “speak the same language” Key Features Compatibility Data Integrity Speed Data Transmission

  4. Receiver 1st word 2nd word Transmitter Parallel Communication • Simultaneous 8-bit transmission • Bits must stay synchronized • Restricted distance to avoid synchronization problems • Theoretically faster (limited by skew) • Hardware easier to implement

  5. Receiver 1st word 2nd word Transmitter Serial Communication • Transfers one bit at a time • Requires only one data line • Slow compared to parallel transmission • Less expensive

  6. Serial vs. Parallel • Serial communication requires less transfer lines • Clock differences between channels • No crosstalk between transmission lines

  7. Applications ATA interface for storage devises (IDE), cable lengths of up to 18” 133 Mbits/sec with 16 bit lines. Serial ATA 1.5Gbits/sec FireWire 8000 Mbits/sec USB 480 Mbits/sec

  8. Synchronization • Asynchronous • Transmission can occur at any time • Receiver is always listening • No idle characters • Data words not locked into system timing • Requires start and stop bits • Synchronous • Data rates determined by clock rates • Continuous transmission to maintain clock synchronization. • Faster

  9. Transmitter and receiver operate independently- Same baud rate- Same data format Requires a start and stop bit to identify each byte of data Asynchronous Serial Transmission

  10. Bit Types Start Bit Data Bits Parity Bit Stop Bit Bit types are used to differentiate between words For MC9S12, 10 or 11 bits Asynchronous Transmission Format

  11. Asynchronous Serial Transmission Start Bit • If line is idle, it continuously sends high (1) logic bit • Each word preceded by start bit • Signals receiver that data is about to be transmitted • Low (0) logic bit Previously HIGH Start Bit Now LOW

  12. Asynchronous Serial Transmission Stop Bit • Stop bit indicates all data has been transmitted • 1 or 2 Stop bits (the MC9S12 uses 1 stop bit) Stop Bit 1 Stop Bit 2 Parity or Bit 7

  13. Asynchronous Serial Transmission Data Bits • The content of the package • Usually 8 bits • LSB sent First Ex: This transmitted word is 10111001, or $B9 LSB MSB Data Bit 0 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 7 Data Bit 1 Data Bit 2 Data Bit 6

  14. Parity Bit • Used to check that all of the set bits were received • Odd parity: bit is set to 1 or 0 to make the sum of all bits odd. • Even parity: makes the sum of all bits even. Transmitted Sum = 4 Start 0 1 1 1 0 1 0 0 Parity Stop Received Sum = 3 Start 0 1 1 0 0 1 0 0 Parity Stop Parity bit sent (1) = Parity of signal received (0)

  15. Asynchronous Serial Transmission Parity Bit • Used to check for errors • Helps verify signal integrity • 2 Types: -Even: makes sum of all high bits INCLUDING parity bit EVEN • -Odd: makes sum of all high bits • INCLUDING parity bit ODD • Can be implemented in hardware by MC9S12C32 Parity Bit (H or L) Data Bit 7

  16. An example of even parity parity start stop 0x52 ? Start Bit Data Bit 0 Data Bit 1 Parity Bit Stop Bit Stop Bit Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7 0 1 1 1 0 0 1 0 1 0 0 1

  17. Transfer Rates • Baud Rate: number of individual states that are transmitted per second. 8 bits of data Start bit + Stop bit_____ 10 bit word

  18. Transmission Rates Example • Example: • Consider baud rate: 4800 baud • 12 bits/word = 1 start bit + 8 data bits + 1 parity bit + 2 stop bits Bit rate = (baud rate)*(8 data bits)/(12 bits total) = 3200 bits/s

  19. Signal Standard • Serial devices convert TTL/CMOS-level signals to higher voltage bipolar signals state 1: -3V to -25V state 0: 3V to 25V

  20. Asynchronous Serial Transmission One Data Word • Four parts per packet Parity Bit Data Bit 1 Data Bit 3 Data Bit 6 HIGH Stop Bit LOW Data Bit 0 Data Bit 2 Start Bit Data Bit 4 Data Bit 5 Data Bit 7

  21. Start bit - Ideal Case (1) logic-zero sample is preceded by three logic-one samples : start-bit qualifiers(2) start-verification samples(3) data samples

  22. Noise (i) Since verification samples RT3 and RT5 are both high, the RT clock count is reset

  23. Noise (ii) Since verification sample RT3 is high, the noise flag is set Data is correctly sampled by RT8-10

  24. Noise (iii) Since verification sample RT5 is high, the noise flag is set Data is correctly sampled by RT8-10

  25. Noise (iv) Since verification samples RT5 and RT7 are both high, no start bit is found

  26. Serial Communication using the MC9S12C32 • Contains receiving and transmitting systems • Includes flags to indicate status of system

  27. SCIBDH and SCIBDL $00C8-9 • SBR[12:0]: Used to determine baud rate for SCI module. Possible values range from 1-8191 SCI Baud Rate = Bus Clock/(16*SCIBR)

  28. SCICR1 $00CA • LOOPS: TXD connected to receiver (1) or normal operation (0) • SCISWAI: SCI enabled (0) or disabled (1) in wait mode • RSRC: In loop mode, receiver connected to transmitter output internally (0) or externally (1) • M: One start bit, eight data bits, one stop bit (0) or One start bit, nine data bits, one stop bit • WAKE: Idle line (0) or address mark (1) wakeup • ILT: Idle character bit count begins after start (0) or stop (1) bit • PE: Parity disabled (0) or enabled (1) • PT: Parity type - even (0) or odd (1)

  29. SCICR2 $00CB • TIE: Transmit data register empty interrupt disabled (0) or enabled (1) • TCIE: Transmit complete interrupt disabled (0) or enabled (1) • RIE: Receiver full or receiver overrun interrupt disabled (0) or enabled (1) • ILIE: Idle line interrupt disabled (0) or enabled (1) • TE: Transmitter disabled (0) or enabled (1) • RE: Receiver disabled (0) or enabled (1) • RWU: Normal operation (0) or receiver wakeup enabled (1) • SBK: No break characters sent (0) or break characters sent (1). Toggling this bit sends one break character out the transmit line

  30. SCISR1 $00CC • TDRE: Transmit data register contains data (0) or is empty (1). Flag cleared by reading SCISR1 with TDRE set and then writing to SCIDRL • TC: Transmit in progress (0) or complete (1) • RDRF: Data not available (0) or available (1) in SCIDR. Flag cleared by reading SCISR1 with TC set and then reading SCIDRL • IDLE: Receiver line not idle (0) or idle (1) • OR: No overrun (0) or data was received before previous data in SCIDR was read (1) • NF: No noise (0) or noise (1) • FE: No framing error (0) or framing error (1) • PF: No parity error (0) or parity error (1)

  31. SCISR2 $00CD • BK13: Break character is 10 or 11 bits (0) or 13 or 14 bits (1) long • TXDIR: TXD is used as an input (0) or output (1) in Single Wire Mode (0) • RAF: No reception in progress (0) or reception in progress (1)

  32. SCIDRH and SCIDRL $00CE-F • Contains received data (when reading) or data to be transmitted (when writing) Note: When accessing using 8-bit instructions, SCIDRH should be written to before SCIDRL is written

  33. Example: Configuring SCI • Write a program that receives data and responds with the 2’s complement of the received data. • Baud Rate: 9600 Clock rate = 8e6 Hz  baud rate = clock rate/(16*BR) BR = clock rate/(16*baud rate) = 8e6/(16*9600) ≈ 52 • Parity: Odd • Data bits: 8, 1 parity bit, so we need to use the 9 bit format

  34. Example: Configuring SCI • SCIBDH = #$00, SCIBDL = #$34 (52 in decimal) • SCICR1 = #$13 - M=1, odd parity enabled Note: parity bit will be determined by hardware • SCICR2 = #$0C - Receiver and transmitter enabled

  35. SCIBDH EQU $00C8 SCIBDL EQU $00C9 SCICR1 EQU $00CASCICR2 EQU $00CB SCISR1 EQU $00CC SCIDRL EQU $00CF ORG $1000 LDAA #$34 STAA SCIBDL ;Set baud rate LDAA #$13 STAA SCICR1 ;Set data format LDAA #$0C STAA SCICR2 ;Enable transmitter and receiver WAIT BRCLR SCISR1,#$20,WAIT ;Check RDRF Flag LDAA SCIDRL ;Get data from SCI data register NEGA ;Perform 2’s complement STAA SCIDRL ;Store result to SCI data reg. BRA WAIT

  36. Questions???

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