Transcript Ultra High Speed Spindle Project Laminate Machinability study

Serial Communication Interface
(SCI)
Ellenor Brown
Howard Liles
Algan Samur
1
Presentation Outline
Types of data transmission

•
•
Parallel
Serial
Serial Communication

•
•
Synchronous
Asynchronous
Baud and Bit Rates
Asynchronous Serial Transmission


•
•
•
•
•


Howard Liles
Ellenor Brown
Start Bit
Data Bit
Stop Bit
Parity Bit
Noise
Algan Samur
SCI Registers
Show two examples of how data words are
transmitted
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Data Transmission
Power supply
circuit
Electronic devices communicating
with each other
Desktop computer
Lights
Turbine generators
Printer
Hard drive
3
Types of Data Transmission
•
Serial Data Transmission
One bit at a time
Receiver (Monitor)
•
Parallel Data Transmission
One word (N bits) at a time
Receiver (printer)
= bits
Word
Transmitter (CPU)
Transmitter (microprocessor)
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Parallel vs. Serial
•
Parallel requires more
transfer lines
•
Bits have to be
synchronized
•
Fast, but expensive
Examples:
• Printer cables
•
Serial requires less transfer
lines
•
Transfers one bit at a time
•
Slow comparatively, but less
expensive
Examples:
USB, Firewire, ethernet
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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
Transmitter
Receiver
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
Transmitter
Word
Receiver
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Comparisons
SYNCHRONOUS
How It Works Clock
Advantages Lower overhead
Greater throughput
Faster
Disadvantages More complex hardware
More expensive
ASYNCHRONOUS
Start and Stop bits
Simple
Cheap hardware
Large overhead
Slower
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Andrew Byrley
Baud and Bit Rates
•
Baud Rate (Bd) is the rate at which Symbols are transferred.
A symbol is a given signaling event
‘Symbols/second’
•
Number of bits per Symbol is Hardware Specific (our hardware
uses 1 baud/bit)
Conversion factor:
•
1 bit = 1 Symbol = 1 baud
Bit rate (bps) - the rate at which bits are transmitted or
“bits/second”
Conversion Equation:
Bit rate (bps) = baud rate × number of bits per baud
 Bits   Sym bols  Bits 
 sec ond    sec ond  *  Sym bol


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Baud and Bit Rates Cont.’d
•
Some bits are data and some are not!
– Remember the start, stop, and parity bits
which are also known as “overhead bits”
•
•
Data throughput can be determined by Characters per second (cps)
Cps = actual rate of data being sent
1 Standard Character = 1 Bit
Characters per second (cps)=Bit rate*(character bits/total bits)
 Characters  Bits   Character_ bits 
 sec ond    sec ond  *  Total _ bits 


•
*Remember CPS is not same as bytes/second. CPS does not include
overhead!
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Baud and Bit Rates Example
Example 1:
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.
Bit rate (bps) = baud rate × number of bits per baud
bps= 9600x2=19200
(cps)=Bit rate*(character bits/total bits)
cps=19200*(8/10)= 15360
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Presentation Outline
Types of data transmission

•
•
Parallel
Serial
Serial Communication

•
•
Synchronous
Asynchronous
Baud and Bit Rates
Asynchronous Serial Transmission


•
•
•
•
•


Howard Liles
Ellenor Brown
Start Bit
Data Bit
Stop Bit
Parity Bit
Noise
Algan Samur
SCI Registers
Show two examples of how data words are
transmitted
11
Asynchronous Serial Communication
• Transmitter and Receiver are independent
• Transmitter sends ‘Start’, ‘Parity’ and ‘Stop’ bits
with each word of data
• Data received between a Stop bit and the next
Start bit is ignored
Stop
Data
Receiver
Transmitter
Parity
Start
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Data Frame Format
•
•
•
•
Start bit – Indicates beginning of data
Data bit – Data being transmitted
Parity bit – Integrity check
Stop bit – Indicates end of data word
• Data frame size: 10 or 11 bits
Stop
Data
Receiver
Transmitter
Parity
Start
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Start Bit
• One bit
• Indicates the beginning of word
• Opposite polarity from idle bit state
– Idle state for HCS12 is 1’s
– Start bit = 0
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Data Bits
• Actual data being transmitted plus a parity
bit
• Most common mode:
– 8-bit transmission
– Used for ASCII character transmission (7-bit
ASCII + 1-bit parity = 8-bit)
• Less common mode:
– 9-bit transmission
– Can be used to send a full byte of data +
parity bit
• HCS12 sends least significant bit (LSB)
first
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Parity Bit
• Used to determine if an error occurred during
data transmission
• Error Detection
– Transmitter calculates proper parity bit
– Receiver calculates parity bit based on data it received
– Receiver compares its parity bit to the one it received
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Evan Johnson
Parity Bit
• 2 types of Parity functionality
• Even Parity
– Parity bit is set to 1 if there is an odd number of
1’s in data bits  # of 1’s becomes even
• Odd Parity
– Parity bit is set to 1 if there is an even number of
1s in data bits  # of 1’s becomes odd)
• Even/Odd Parity is set by user on HCS12
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Evan Johnson
Stop Bit
•
•
•
•
1 or 2 bits
Used due to asynchronous nature
Directly after the parity bit
Stop bit is the same as the polarity of the
data-line’s idle state
– Idle state for HCS12 = all 1’s
– Stop bits = 1
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Asynchronous Data Transmission
• Example 1:
– Hex# 4A16 is to be sent with one start bit, even parity,
8-bit data length and one stop bit
– 4A16 = 0100 10102
Start Bit
0
Data Bit 0 Data Bit 1 Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7
0
1
0
1
0
0
1
0
Parity Bit
1
Stop Bit
1
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Asynchronous Data Transmission
• Example 2:
– Hex# B416 is to be sent with one start bit, even parity,
8-bit data length and one stop bit
– B416 = 1011 01002
Start Bit
0
Data Bit 0
0
Data Bit 1
0
Data Bit 2 Data Bit 3
1
0
Data Bit 4
1
Data Bit 5
1
Data Bit 6 Data Bit 7
0
1
Parity Bit
0
Stop Bit
1
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Asynchronous Data Transmission
• Example 3:
– Hex# B416 is to be sent with one start bit, odd parity, 8bit data length and one stop bit
– B416 = 1011 01002
Start Bit
0
Data Bit 0
0
Data Bit 1 Data Bit 2 Data Bit 3 Data Bit 4 Data Bit 5 Data Bit 6 Data Bit 7 Parity Bit
0
1
0
1
1
0
1
1
Stop Bit
1
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Error sources
• Frame shift
– Detected when a logic 0 is accepted as the stop
bit
• Overrun
– Software fails to read the SCI data register
before the shift register receives the next frame
• Noise
– SCI detects noise on the receiver input
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Framing 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:
“4” bit is skipped and
stop bit is one bit
before it should be
1 2 3
4 5 6
7
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Overrun
SOFTWARE
REGISTER
RECEIVER
• Software fails to read
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
TRANSMITTER
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Noise Detection
• SCI detects noise on the receiver input
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Presentation Outline
Types of data transmission

•
•
Parallel
Serial
Serial Communication

•
•
Synchronous
Asynchronous
Baud and Bit Rates
Asynchronous Serial Transmission


•
•
•
•
•


Howard Liles
Ellenor Brown
Start Bit
Data Bit
Stop Bit
Parity Bit
Noise
SCI Registers
Coding example
Algan Samur
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SCI Baud Rate Registers
SCIBDH & SCHBDL - $00C8-$00C9
•
•
•
•
13-Bits register determines SCI Baud rate
Baud rate generator is disabled until TE or RE bit is set for the first
time after reset.
Baud rate generator is turned off when this register contains $0000
Note: Writing to SCIBDH has no effect w/out writing to SCIBDL
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Implementation Specific Features (S12SCIV2)
 13-bit baud rate selection
 8- or 9-bit data format
 Separately enabled transmitter and receiver
 Programmable transmitter output parity
 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
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SCI Control Register 1
SCICR1 - $00CA
•
•
•
M (data format mode) - 0: 8 data bits,
- 1: 9 data bits.
- Both use 1 start bit and 1 stop bit
PE (parity enable) – 0: Off, 1: On
PT (parity type) – 0: Even, 1: Odd
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SCI Control Register 2
SCICR2 - $00CB
•
TIE (transmit interrupt enable) – 0: disables interrupts for transmit data
register empty, 1: enables
•
TCIE (transmit complete interrupt enable) – 0: disables interrupts for
transmit complete, 1: enables
•
RIE (receiver interrupt enable) – 0: disables interrupts for receiver full and
overrun , 1: enables
•
ILIE (idle line interrupt enable) – 0: disables interrupts for idle line, 1:
enables
•
TE (transmit enable) – 0: disable transmitter, 1: enable
•
RE (receiver enable) – 0: disable receiver, 1: enable
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SCI Status Register 1
SCISR1 - $00CC
•
•
•
•
•
•
Read only register
Can be used to provide input to the microcontroller for
generation of SCI interrupts
TDRE (transmit data register empty) – 0: No byte
transferred,1: byte successfully transferred to transmit
shift register
TC (transmit complete flag) – 0: transmission in
progress, 1: no transmission in progress
RDRF (receive data register full) – 0: no data in data
register, 1: data in data register
IDLE (idle flag) – 0: receiver input is active, 1:
receiver input has become idle
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SCI Status Register 1
SCISR1 - $00CC
• OR (overrun) – 0: no overrun, 1: overrun
(overrun happens when new data is received
before old data is read)
• NF (noise flag) – 0: disable, 1: enable
• FE (framing error flag) – 0: disable, 1: enable
• PF (parity error) – 0: No parity error, 1: parity
error
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SCI Status Register 2
SCISR2 - $00CD
•
•
•
BK13 (break transmit character length) – 0: 10 or 11 bit, 1: 13 or 14
bit
TXDIR (transmitter pin direction) – 0: TXD pin used as input,
1: TXD pin used as output. (used only in single wire mode)
RAF (receiver active flag) – 0: no reception in progress, 1: reception
in progress
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SCI Data Registers
SCIDRH &SCIDRL - $00CE - $00CF
•
•
•
SCIRDL contains incoming bytes of data from serial port
R8 – bit 8 of received 9-bit data
T8 – bit 8 of transmitted 9-bit data
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SCI is easy
 SCI module makes it easy to send/receive data
 SCI module encodes data into standard NRZ
format!
 Hardest part is setting up baud rate
 Can use either polling or interrupt based logic
to drive SCI
 SCIDRH/SCIDRL are like two registers in one.
• Read this register to receive data
• Write to this register to send data
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Example
• First, calculate baud rate. Assume
8MHz bus and desired baud rate is
9600
SCI baud rate 
SCI module clock
16  SCIBR[12 : 0]
• SCI module runs at bus speed
• Desired value for SCIBR is 52
• You will have some error margin
– Exact solution is 52.0833
– Actual baud rate is 9615.3 (0.160% error)
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Example
 Write SCIBR ($0034) to SCIBDH/SCIBDL
 For 8-bit, no parity, no interrupts, default
values will work
 Simply enable transmit and receive in
SCICR2
 Read from SCIDRL to receive 8-bit data
 Write data to SCIDRL to send 8-bit data
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Code Example
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Code Example
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#include <hidef.h>
/* common defines and macros */
#include <mc9s12c32.h> /* derivative information */
#pragma LINK_INFO DERIVATIVE "mc9s12c32"
MISC = 0x03;
PEAR = 0x0C;
MODE = 0xE2;
void SCI_init(void){
int BR = 0x0034;
SCIBDH = BR>>8; //stores high Byte
SCIBDL = BR; //stores low Byte
SCICR2 = 0x0C; //sets TE and RE to 1
}
//Call function to setup SCI
SCI_init();
//Main loop
while(1) {
char SCI_getByte(void){
while (!(SCISR1_RDRF))
;//waits FOREVER until receive register is full
return SCIDRL;
}
SCI_sendByte(data);
} /* loop forever */
/* please make sure that you never leave this function */
char data = SCI_getByte();
}
void SCI_sendByte(char data){
while (!(SCISR1_TDRE))
;//waits FOREVER until transmit register is empty
SCIDRL = data;
//return void;
}
void main(void) {
//variable declarations must go at beginning
/* put your own code here */
EnableInterrupts;
//required code as per instructions
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Thank You!
Any Questions?
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