Transcript Serial Communication Interface 1 Brian Guerriero

Serial Communication
Interface
Brian Guerriero
Jon Rogers
Robert Thiets
October 26, 2006
ME 6405 Mechatronics
Serial Communication Interface
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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
Receiver
♦Requires separate data
lines
♦Bits must stay synchronized
♦Fast
♦Expensive
♦Example: Printer
connections
One Word
Transmitter
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Types of Data Transmission
Serial Data Transmission
♦Transfers one bit at a time
Receiver
♦Requires only one data
line Bits must stay
synchronized
♦Slow compared to parallel
transmission
♦Less Expensive
One Word
♦Example: USB
Transmitter
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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
BitRate ( Bit / s)
Bd ( Symbol / s) 
Bits / Symbol
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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
Data
Bit 1
Data
Bit 3
Parity
Bit
Data
Bit 6
HIGH
Stop Bits (2)
LOW
Start
Bit
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Data
Bit 0
Data
Bit 2
Data Data
Bit 4 Bit 5
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Data
Bit 7
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Asynchronous Serial Transmission
Start Bits
♦Start bit drops from
1 to 0 to signal start
of transmission
Previously
HIGH
Start
Bit
Now LOW
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Asynchronous Serial Transmission
Data Bits
♦The content of the
package
Ex: This transmitted word
is 10111001,
or $B9
♦Usually 8 bits
♦LSB sent First
LSB
Data
Bit 0
Data Data Data
Bit 3 Bit 4 Bit 5
Data
Bit 1
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MSB
Data
Bit 2
FLOW
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Data
Bit 7
Data
Bit 6
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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
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Parity
Bit
(H or L)
Data
Bit 7
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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
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Asynchronous Serial Transmission
Noise
♦ Causes errors in reading data
♦ Start bit is misread and begins
reading too early
Stop
Bit
NOISE
Start
Bit
Goes LOW
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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
Address:
Read:
Write:
Reset:
U = Unaffected
$102B
Bit 7
0
TCLR
0
6
5
4
0
SCP1
SCP0
0
0
0
3
2
0
SCR2
RCKB
0
U
1
Bit 0
SCR1
SCR0
U
U
♦ 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
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HC11 SCI Registers
SCCR1 Register
Address:
Read:
Write:
Reset:
U = Unaffected
$102C
Bit 7
R8
U
6
T8
U
5
0
0
4
3
M
WAKE
0
0
2
0
1
0
Bit 0
0
0
0
0
♦ 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 Register
Address:
Read:
Write:
Reset:
U = Unaffected
$102D
Bit 7
6
5
4
3
2
1
Bit 0
TIE
TCIE
RIE
ILIE
TE
RE
RWU
SBK
0
0
0
0
0
0
0
0
♦ 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 Register
Address:
Read:
Write:
Reset:
U = Unaffected
$102E
Bit 7
TDRE
6
TC
5
RDRF
4
IDLE
3
OR
2
NF
1
FE
Bit 0
0
1
1
0
0
0
0
0
0
♦ 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 Register
Address:
Read:
Write:
Reset:
U = Unaffected
$102F
Bit 7
R7
T7
6
R6
T6
5
R5
T5
4
3
2
R4
R3
R2
T4
T3
T2
Unaffected by rest
1
R1
T1
Bit 0
R0
T0
♦ 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
♦
♦
Let’s say we want to transmit hex number 2C at a Baud rate
of 1200
First set up variables and set Baud rate:
MAIN EQU $1040
SCCR2 EQU $102D
BAUD EQU $102B
SCSR EQU $102E
SCDR EQU $102D
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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
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Examples of SCI
Transmit – Set Baud Rate
BAUD
♦
TCLR
SCP2
SCP1
SCP0
RCKB
SCR2
SCR1
SCR0
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!
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Examples of SCI
Transmit !
ORG MAIN
LDAA #$33
STAA BAUD
LDAA #$08
STAASCCR2
LOOP
LDAA
STAA
CHECK LDAA
ANDA
CMPA
BNE
SWI
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#$2C
SCDR
SCSR
#$C0
#$C0
CHECK
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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
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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
October 26, 2006
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
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Examples of SCI
Receive!
CHECK
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ORG
LDAA
STAA
LDAA
STAA
MAIN
#$33
BAUD
#$04
SCCR2
This sets bits like in previous
slide
Write to the Baud register
Set the Receive Enable bit high
Write to SCCR2
LDAA
ANDA
CMPA
BNE
LDAA
STAA
SWI
SCSR
#$20
#$20
CHECK
SCDR
STORE
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
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Questions
?
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