1 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Brian Guerriero Jon Rogers Robert Thiets

2 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Presentation Outline  Types of Data Transmission Parallel Serial  Serial Communication Synchronous Asynchronous  Baud and Bit Rates  Asynchronous Serial Transmission  Serial Communication With the HC11  Examples of data words are transmitted

3 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Types of Data Transmission Parallel Data Transmission ♦Simultaneous transmission ♦Requires separate data lines ♦Bits must stay synchronized ♦Fast ♦Expensive ♦Example: Printer connections Transmitter Receiver One Word

4 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Types of Data Transmission Serial Data Transmission ♦Transfers one bit at a time ♦Requires only one data line Bits must stay synchronized ♦Slow compared to parallel transmission ♦Less Expensive ♦Example: USB Transmitter Receiver One Word

5 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Serial Data Communication ♦Two basic types of Serial Data Communication: –Synchronous Communication –Asynchronous Communication

6 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Synchronous Communication ♦Transmitter and receiver have their clocks synchronized ♦Data rates are dependent on clock rates ♦Continuously transmitting characters to remain in sync.

7 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Communication ♦NO synchronization –No need to send idle characters ♦Transmitter and receiver operate independently –Transmitter can send data at any time –Receiver is always ready to accept data ♦Requires a start and stop bit to identify each byte of data ♦How does receiver know that data is arriving? –If the line is idle, it is sending a constant ‚1‘ (mark state) –The receiver is able to recognize a jump from ‚1‘ to ‚0‘ with the start bit and is alerted that data is about to be sent.

8 October 26, 2006ME 6405 MechatronicsSerial Communication Interface BIT RATE (Bit/s) ♦Number of data bits (High/Low V) transmitted per second. Example of Windows Bit Rates

9 October 26, 2006ME 6405 MechatronicsSerial Communication Interface BAUD RATE (Bd) ♦Rate of “Symbol” transfer ♦Each symbol > 1 bit ♦Symbol type and size determined by quality of hardware

10 October 26, 2006ME 6405 MechatronicsSerial Communication Interface BAUD RATE (Bd) Example Calculations ♦Consider baud rate: 4800 baud ♦12 bits/word = 1 start bit + 8 data bits + 1 parity bit + 2 stop bits –Bit time = 1/(baud rate) = 1/4800baud = 0.208ms/bit –Word time = (12 bits)*(bit time) = 2.5ms –Word rate = 1/(word time) = 400 words/s –Bit rate = (word rate)*(8 data bits) = 3200 bits/s

11 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission ♦Bits are transmitted in a specified format ♦Defined by settings on transmitter and receiver: -Start Bit -Data Bits -Parity Bits -Stop Bits Example of Windows setting

12 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission One Data Package ♦Four parts per package Start Bit Data Bit 0 Data Bit 1 Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7 Parity Bit Stop Bits (2) HIGH LOW

13 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission Start Bits ♦Start bit drops from 1 to 0 to signal start of transmission Start Bit Previously HIGH Now LOW

14 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission Data Bits ♦The content of the package ♦Usually 8 bits ♦LSB sent First Ex: This transmitted word is , or $B9 Data Bit 2 Data Bit 0 Data Bit 1 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7 LSBMSB FLOW

15 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission Parity Bit ♦ Used to check for errors ♦ Helps verify signal integrity ♦ 2 Types: -Even: makes sum of all bits INCLUDING parity bit EVEN -Odd: makes sum of all bits INCLUDING parity bit ODD ♦ Not applicable to HC11 Data Bit 7 Parity Bit (H or L)

16 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission Stop Bit ♦ Stop bit indicates all data has been transferred ♦ 1 or 2 Stop bits Stop Bit 1 Stop Bit 2 Parity or Bit 7

17 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Asynchronous Serial Transmission Noise ♦ Causes errors in reading data ♦ Start bit is misread and begins reading too early Start Bit NOISE Goes LOW Stop Bit

18 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers ♦5 Main Registers: –BAUD: Sets bit rate for SCI –SCCR1: Sets control bits for the 9-bit character format and the receiver wake up feature –SCCR2: Main control register –SCSR: Status Register –SCDR: Main Data Register

19 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers BAUD Register ♦ Used to set the bit rate of the SCI system – TCLR: Clear baud rate timing chain bit – SCP1: SCP0 – Baud rate pre-scale select bits – RCKB: SCI baud rate clock test bit – SCR2: SCR0 – SCI baud rate select bits Address:$102B Bit Bit 0 Read: 00 Write: TCLRRCKB Reset:00000UUU U = Unaffected SCR1SCR0SCP00SCP1SCR2

20 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers SCCR1 Register ♦ Contains control bits related to the 9-bit data character format and the receiver wake up feature – R8: Receive data bit 8 – T8: Transmit data bit 8 – M: SCI character length bit – WAKE: Wakeup method select bit – Bits 0, 1, 2 & 5: Not used (always 0)

21 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers SCCR2 Register ♦Main control register for SCI sub-system –TIE: Transmit interrupt enable bit –TCIE: Transmit complete interrupt enable bit –RIE: Receive interrupt enable bit –ILIE: Idle-line interrupt enable bit –TE: Transmit enable bit –RE: Receive enable bit –RWU: Receiver wakeup bit –SBK: Send break bit

22 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers SCSR Register ♦SCI status register – TDRE: Transmit data register empty bit – TC: Transmit complete bit – RDRF: Receive data register full bit – IDLE: Idle-line detect bit – OR: Overrun error bit – NF: Noise flag – FE: Framing Error bit – Bit 0: is not used (always 0)

23 October 26, 2006ME 6405 MechatronicsSerial Communication Interface HC11 SCI Registers SCDR Register ♦SCI data register – Two separate registers – When SCDR is read, the read-only RDR is accessed – When SCDR is written, the write-only TDR is accessed – R7 - R0: Read bits – T7 - T0: Write bits

24 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Auxiliary Port D ♦SCI uses the 2 least significant bits of Port D ♦These bits are used for receiving and transmitting data ♦Data direction register does not control Port D while SCI is in use but it is important since it will have control when the SCI operation is aborted ♦SPCR register controls the Port D wire-OR mode bit, which controls the driver functions of the Port D pins, even if they are being used by the SCI

25 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Wake Up ♦M68HC11 supports a receiver wake up function, which is intended for systems having more than one receiver ♦The transmitting device directs messages to an individual receiver or group of receivers by passing addressing information in the initial byte ♦Receivers not addressed activate the receiver wakeup function –This makes these receivers dormant for the remainder of the unwanted message ♦Wake up mode is enable by writing a 1 to the RWU bit in the SCCR2 register

26 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Wake Up ♦Two methods of Wakeup –Address-Mark Wakeup Most significant bit is used to indicate if the message is data(0) or address(1) All receivers wake up if the bit is 1 and check to see if the message is for them ♦Send Breaks –Break characters are character-length periods where the TxD line goes to 0 –Character length is influenced by the M bit in the SCCR1 M = 0 – All characters are 10 bit times long M = 1 – all characters are 11 bit times long –Break characters have no start and stop bits

27 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Examples of SCI Transmit - Configuration MAIN EQU $1040 SCCR2 EQU $102D BAUD EQU $102B SCSR EQU $102E SCDR EQU $102D Assemble code starting here Address of SCI control register 2 Address of Baud rate control register Address of SCI status register Address of SCI data register ♦ Let’s say we want to transmit hex number 2C at a Baud rate of 1200 ♦ First set up variables and set Baud rate:

28 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Examples of SCI Transmit – Set Baud Rate ♦How to set the Baud rate: –Crystal Frequency = 8 MHz –First, set BAUD bits SCP2 =1 and SCP1 = 1 Divides crystal freq. by 13 8 MHz ÷ 13 ≈ 9600 –Then set SCR2 = 0, SCR1 = 1, SCR0 = 1 Divides result by ÷ 8 = 1200 See tables on P ! TCLRSCP2SCP1SCP0RCKBSCR2SCR1SCR0 BAUD

29 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Examples of SCI Transmit ! ORG MAIN LDAA #$33 STAA BAUD LDAA #$08 STAASCCR2 LOOP LDAA #$2C STAA SCDR CHECK LDAA SCSR ANDA #$C0 CMPA #$C0 BNE CHECK SWI This sets bits like in last slide Write to the Baud register Set the Transmit Enable bit high Write to SCCR2 Put you data to transmit here Store it in the SCI data register Load the status register to Acc A Check to see if Transmit Complete flag is set If it is not, loop and keep checking If it is, we’re done

30 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Examples of SCI Receive- Configuration ♦Once again, Baud rate of 1200 ♦Set up things in a similar way: MAIN EQU $1041 SCCR2 EQU $102D BAUD EQU $102B SCSR EQU $102E SCDR EQU $102F STORE EQU $1040 Assemble code starting here Address of SCI control register 2 Address of Baud rate control register Address of SCI status register Address of SCI data register Address of place to store incoming data

31 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Examples of SCI Receive! ORG MAIN LDAA #$33 STAA BAUD LDAA #$04 STAA SCCR2 CHECK LDAA SCSR ANDA #$20 CMPA #$20 BNE CHECK LDAA SCDR STAA STORE SWI This sets bits like in previous slide Write to the Baud register Set the Receive Enable bit high Write to SCCR2 Load the status register into Acc A Check to see if RDRF flag is set (Receive Data Register Full) If not, keep checking until it is When data has been received, store it

32 October 26, 2006ME 6405 MechatronicsSerial Communication Interface Questions ?