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Swipe Card Reader w/ Liquid Crystal Display. Embedded Systems Interfacing Laboratory. Overview. Background Task 0 – Clean Up Motor Feedback Lab Task 1 -- Understand Data Stream w/ MSO Task 2 -- Basic ISR w/ Strobe Count and Ones Count Task 3 -- Capture Data with ISR

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swipe card reader w liquid crystal display

Swipe Card Reader w/ Liquid Crystal Display

Embedded Systems Interfacing Laboratory

overview
Overview
  • Background
  • Task 0 – Clean Up Motor Feedback Lab
  • Task 1 -- Understand Data Stream w/ MSO
  • Task 2 -- Basic ISR w/ Strobe Count and Ones Count
  • Task 3 -- Capture Data with ISR
  • Task 4 -- Decode, check, and display data/errors
mcr 175 1r swipe card reader
MCR-175-1R Swipe Card Reader

Color Signal Explorer-16

BLACK GROUND Vss

RED +5V Vdd

YELLOW /CARD DETECT RD14

BLUE /DATA RE9

GREEN /STROBE RE8

task 1 start sentinel
Task 1 -- Start Sentinel

RTZ

Encoding

1 2 4 8 P 1 2 4 8 P 1 2 4 8 P 1 2 4 8 P 1 2 4 8 P

1

2

‘6’

2

‘B’

Remember data comes in one bit at a time (per interrupt).

task 1 end sentinel
Task 1 -- End Sentinel

1 2 4 8 P 1 2 4 8 P 1 2 4 8 P

No Ones

CHAR

LRC

‘F’

task 2 basic interrupt service routine template
Task 2 -- Basic Interrupt Service Routine Template

void __attribute__((interrupt,no_auto_psv)) _INT1Interrupt(void) {

  INT1IF=0;

// insert code here

}

void main(void){

//Initialize ports & interrupt enable bits

endless:

// Process

// Display stb_cnt on bargraph;

goto endless;

}

task 2 initswipe
Task 2 -- initSwipe
  • Card detect as input
  • Data as input
  • INTCON2bits.INT1EP=?
  • IFS1bits.INT1IF=0
  • IEC1bits.INT1IE=1
  • Optional IPL
    • _IPL < _INT1IP
task 3 capture data
Task 3 -- Capture Data

ERROR

LEAD-

ING

First One

CHARAC-

TER

CD

default

“00000”

NEW

STROBE

Conversion

Complete

TRAIL-

ING

DECODE

task 3 state type
Task 3 – STATE_TYPE

enum STATE_TYPE {NEW,LEADING,CHARACTER,TRAILING,DECODE,ERROR};

enum STATE_TYPE state=NEW;

unsigned char bit_cnt=0;

unsigned char char_cnt=0;

unsigned char one_cnt=0;

unsigned char character;

unsigned char buffer[40];

task 3 switch statement
Task 3 -- Switch Statement

•••••

switch(state){

case NEW: •••••

break;

case LEADING: •••••••

default:

state = ERROR;

}

You write CHARACTER state code

task 4 parity lrc
Task 4 -- Parity & LRC

Hex Binay

Value Value

WithoutWithout

P 8 4 2 1 Parity Parity



Start Sentinel: B 0 1 0 1 1 B  1 0 1 1

1 0 0 0 0 1 1  0 0 0 1

2 0 0 0 1 0 2  0 0 1 0

3 1 0 0 1 1 3  0 0 1 1

End Sentinel: F 1 1 1 1 1F 1 1 1 1

LRC 4 0 0 1 0 0 4 0 1 0 0

0 0 0 0 0

Odd Parity

Even

Parity

Easier yet bitwise “exclusive-or” all including LRC = 0

task 4 mainline
Task 4 -- Mainline
  • Display the message “Swipe card…” on first line of LCD
  • Wait for state to go to DECODE.
  • Clear display
  • Display data buffer on first and second line of LCD
  • Display one of the following on the bargraph
    • “No errors…”
    • “Start error…”
    • “Parity error…”
task 4 mainline continued
Task 4 -- Mainline Continued
    • “Stop error…”
    • “LRC error…”
  • Prepare for next card swipe by setting state to NEW.
  • You can do the four error checks in main or the interrupt service routine.
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