1 october 26, 2006me 6405 mechatronicsserial communication interface brian guerriero jon rogers...
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1October 26, 2006 ME 6405 Mechatronics Serial Communication Interface
Serial Communication Interface
Brian GuerrieroJon Rogers
Robert Thiets
2October 26, 2006 ME 6405 Mechatronics Serial 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
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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
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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
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Serial Data Communication
♦ Two basic types of Serial Data Communication:– Synchronous Communication– Asynchronous Communication
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Synchronous Communication
♦ Transmitter and receiver have their clocks synchronized
♦ Data rates are dependent on clock rates♦ Continuously transmitting characters to remain in
sync.
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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.
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BIT RATE (Bit/s)
♦Number of data bits (High/Low V) transmitted per second.
Example of Windows Bit Rates
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BAUD RATE (Bd)
♦Rate of “Symbol” transfer
♦Each symbol > 1 bit
♦Symbol type and size determined by quality of hardware
SymbolBits
sBitBitRatesSymbolBd
/
)/()/(
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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
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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
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Asynchronous Serial Transmission
One Data Package
♦Four parts per package
Start Bit
DataBit 0
DataBit 1
DataBit 2
DataBit 3
DataBit 4
DataBit 5
DataBit 6
DataBit 7
ParityBit
Stop Bits (2)HIGH
LOW
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Asynchronous Serial Transmission
Start Bits
♦Start bit drops from 1 to 0 to signal start of transmission
Start Bit
Previously HIGH
Now LOW
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Asynchronous Serial Transmission
Data Bits
♦The content of the package
♦Usually 8 bits
♦LSB sent First
Ex: This transmitted word is 10111001,
or $B9
DataBit 2
DataBit 0
DataBit 1
DataBit 3
DataBit 4
DataBit 5
DataBit 6
DataBit 7
LSB MSB
FLOW
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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
DataBit 7
ParityBit (H or L)
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Asynchronous Serial Transmission
Stop Bit
♦ Stop bit indicates all data has been transferred
♦ 1 or 2 Stop bits
StopBit 1
StopBit 2
Parity or Bit 7
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Asynchronous Serial Transmission
Noise
♦ Causes errors in reading data
♦ Start bit is misread and begins reading too early
Start BitNOISE
Goes LOW
Stop Bit
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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
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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: $102BBit 7 6 5 4 3 2 1 Bit 0
Read: 0 0Write: TCLR RCKBReset: 0 0 0 0 0 U U U
U = Unaffected
SCR1 SCR0SCP00 SCP1 SCR2
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HC11 SCI Registers
SCCR1 RegisterAddress: $102C
Bit 7 6 5 4 3 2 1 Bit 0Read: R8 0 0 0 0Write:Reset: U U 0 0 0 0 0 0
U = Unaffected
WAKET8 M
♦ 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)
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HC11 SCI Registers
SCCR2 RegisterAddress: $102D
Bit 7 6 5 4 3 2 1 Bit 0Read:Write:Reset: 0 0 0 0 0 0 0 0
U = Unaffected
RWU SBKTIE TETCIE RIE ILIE RE
♦ 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
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HC11 SCI Registers
SCSR RegisterAddress: $102E
Bit 7 6 5 4 3 2 1 Bit 0Read: TDRE TC RDRF IDLE OR NF FE 0Write:Reset: 1 1 0 0 0 0 0 0
U = Unaffected
♦ 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)
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HC11 SCI Registers
SCDR RegisterAddress: $102F
Bit 7 6 5 4 3 2 1 Bit 0Read: R7 R6 R5 R4 R3 R2 R1 R0Write: T7 T6 T5 T4 T3 T2 T1 T0Reset:
U = UnaffectedUnaffected by rest
♦ 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
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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
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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
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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
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Examples of SCI
Transmit - Configuration
MAIN EQU $1040SCCR2 EQU $102DBAUD EQU $102BSCSR EQU $102ESCDR EQU $102D
Assemble code starting hereAddress of SCI control register 2Address of Baud rate control registerAddress of SCI status registerAddress 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:
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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 9600 ÷ 8 = 1200
See tables on P. 29-30!
TCLR SCP2 SCP1 SCP0 RCKB SCR2 SCR1 SCR0BAUD
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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 slideWrite to the Baud registerSet the Transmit Enable bit highWrite to SCCR2
Put you data to transmit hereStore it in the SCI data register
Load the status register to Acc ACheck to see if Transmit Complete flag is set
If it is not, loop and keep checkingIf it is, we’re done
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Examples of SCI
Receive- Configuration
♦ Once again, Baud rate of 1200♦ Set up things in a similar way:
MAIN EQU $1041SCCR2 EQU $102DBAUD EQU $102BSCSR EQU $102ESCDR EQU $102FSTORE EQU $1040
Assemble code starting hereAddress of SCI control register 2Address of Baud rate control registerAddress of SCI status registerAddress of SCI data registerAddress of place to store incoming data
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Examples of SCI
Receive!
ORG MAINLDAA #$33STAA BAUDLDAA #$04STAA SCCR2
CHECK LDAA SCSRANDA #$20CMPA #$20BNE CHECKLDAA SCDRSTAA STORESWI
This sets bits like in previous slideWrite to the Baud registerSet the Receive Enable bit highWrite to SCCR2
Load the status register into Acc ACheck to see if RDRF flag is set(Receive Data Register Full)If not, keep checking until it isWhen data has been received, store it
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Questions
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