Proximity Reader (Weigand) aka RFID

Well after a good day of getting used to the basic I/O of some of the PICs I have I decided to tackle a RFID card reader project. The use of an oscilloscope was definitely a huge help in the process. It's taken me about 4 days to get the program to it's current state, really the only thing left to do is replace the "TODO" comments with actual code, but I'll leave that up to whoever actually uses the code. Note: LCD code was taken from pic16.com examples so I can't take credit for that; the original was written in C and I had to port it over to PBP

Here's the hardware:
QL200 Pic Development Board (ebay)
Mini Weigand 26 Card Reader (ebay)
Trine electric strike (16-24 volt model but works fine at 12VDC) (ebay)
PIC 16F8778A (came with the board)
LCD screen (not serial interfaced / connected to portD[0:7])
IRF520 -- interface between PIC output and strike, the strike needs at least 500mA to activate!
RA4 has a pullup resistor

Code:

---

'''''''''''''''''''''''''''''''
''' Set up I/O
'''''''''''''''''''''''''''''''
ADCON1    = %00000111 
TRISA          = %00000000
TRISD          = %00000000
TRISC      = %11111111
'''''''''''''''''''''''''''''''
''' Tell PBP we are running
''' at 20 MHz
'''''''''''''''''''''''''''''''
DEFINE osc 20
''''''''''''''''''''''''''
'    Initialize EEPROM  '
''''''''''''''''''''''''''
' 33971 33972 33973 other are 65535 i.e FF or uninitialized
DATA @0, 179, 132, 180, 132, 181, 132, 255, 255, 255, 255
DATA @10, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255
DATA @20, 03 'Number of users stored in EEPROM
'''''''''''''''''''''''''''''''
''' LCD Screen I/O
'''''''''''''''''''''''''''''''
rs var PortA.1 'Register Select (Data/Command Register)
rw var PortA.2 'Register Read/Write
e  var PortA.3 'LCD Enable
'DB0 - DB7 located at PortD
'''''''''''''''''''''''''''''''
''' Temporary variables
'''''''''''''''''''''''''''''''
x var byte
i var byte
'''''''''''''''''''''''''''''''
''' Most important variables
'''''''''''''''''''''''''''''''
CardRead        var bit
GoodCard        var bit
PgrmMode        var bit
BitCount        var byte
CardWordH        var word    'Need two words for 26 bit card
CardWordL        var word
Users                var word[10] 'Word array of users containing only user codes
NumUsers        var byte
SiteCode        con 209
StrikeTime        con 5000 'time in ms to unlock door
'''''''''''''''''''''''''''''''
''' Weigand reader I/O
'''''''''''''''''''''''''''''''
Data0                var PORTC.0
Data1                var PORTC.1
Strike                var PORTA.5
Buzzer                var PORTA.0
GreenLED        var PORTA.4
PgrmSw                var PORTC.2
'''''''''''''''''''''''''''''''
''' Initialize variables
''' Card Users and
''' I/O ports For first use
'''''''''''''''''''''''''''''''
InitUsers:
Read 20, NumUsers
if NumUsers = $FF then NumUsers = 0 'Just in case EEPROM has nothing.
For i = 0 to NumUsers*2 'Bytes are written reversed For easy reading ;-)
        Read i, Users.lowbyte(i)
Next i
BitCount = 0
CardRead = 0
CardWordL = 0
CardWordH = 0
LOW strike
HIGH buzzer
HIGH GreenLed
'''''''''''''''''''''''''''''''
''' Set up LCD and splash screen
'''''''''''''''''''''''''''''''
GoSub LCD_init
GoSub write_splash
'''''''''''''''''''''''''''''''
''' Here is the main program
'''''''''''''''''''''''''''''''
loop:
If PgrmSW = 0 then
        If CardRead = 1 Then
                PORTD = %00000001 'clr screen
                GoSub lcd_cmd
                For i = 15 to 0 step -1 'This loop writes the Site Code to Line 1
                        x = 0
                        x = CardWordH.0(i)
                        x = x | %00110000 'Make x a character
                        GoSub lcd_data
                Next i
                PORTD = %11000000 'set the 2nd line display address
                GoSub lcd_cmd
                Pause 100
                For i = 15 to 0 step -1 'This loop writes the User Code to Line 2
                        x = 0
                        x = CardWordL.0(i)
                        x = x | %00110000 'Make x a character
                        GoSub lcd_data
                Next i
                CardRead = 0
                GoodCard = 0
                For i = 0 to NumUsers - 1
                        If CardWordL = Users[i] and CardWordH = SiteCode Then
                                HIGH  Strike 'Activate electric strike
                                LOW  GreenLED 'Green LED activated on gnd
                                Pause StrikeTime
                                PORTD = %00000001 'clr screen
                                GoSub lcd_cmd
                                For i = 0 to 15
                                        LOOKUP i, ["CARD ACCEPTED  "], x
                                        GoSub lcd_data
                                Next i
                                LOW  Strike
                                HIGH  GreenLED
                                GoodCard = 1
                        EndIf
                Next i
                If GoodCard = 0 then 'Invalid Card
                        For i = 0 to 2 'Beep 3 times
                                LOW  Buzzer
                                Pause 100
                                HIGH  Buzzer
                                Pause 100
                        Next i
                EndIf
                CardWordH = 0
                CardWordL = 0
        EndIf
        GoSub ReadCard
Else
        'Init Program Mode
        While PgrmSw = 1:        Wend
        PgrmMode = 1
        PORTD = %00000001 'clr screen
        GoSub lcd_cmd
        For i = 0 to 15
                LOOKUP i, ["Program Mode    "], x
                GoSub lcd_data
        Next i
        While PgrmMode = 1
                If PgrmSW = 1 then
                        While PgrmSw = 1:        Wend
                        PgrmMode = 0
                EndIf
                'Main Program Mode Menu Here
        Wend
        'Exit Program Mode / UPDATE EEPROM
        PORTD = %00000001 'clr screen after exiting program mode
        GoSub lcd_cmd
EndIf
Goto loop

'For Program Mode:
                'For i = 0 to 1 'Bytes are written reversed For easy reading later ;-)
                        'write j, CardWordL.lowbyte(i)
                        'j = j + 1
                'Next i

'''''''''''''''''''''''''''''''
''' Card Reading subroutine
'''''''''''''''''''''''''''''''
ReadCard:
if Data0 = 1 and Data1 = 1 then Return
ReadLoop:
        If Data0 = 0 Then
                If BitCount > 9 Then ' Bits 0 - 9 go to CardWordH, 10-25 go to CardWordL
                        CardWordL = CardWordL << 1
                        CardWordL.0 = 0
                Else
                        CardWordH = CardWordH << 1
                        CardWordH.0 = 0
                EndIf
                BitCount = BitCount + 1
                While Data0 = 0:        Wend
        EndIf
        If Data1 = 0 Then
                If BitCount > 9 Then
                        CardWordL = CardWordL << 1
                        CardWordL.0 = 1
                Else
                        CardWordH = CardWordH << 1
                        CardWordH.0 = 1
                EndIf
                BitCount = BitCount + 1
                While Data1 = 0 :        Wend
        EndIf
        If BitCount < 26 Then
'TODO: Make sure that we don't end up in an infinite loop here; utilize the i counter
                i = i + 1
                Goto ReadLoop
        Else
                BitCount = 0
'TODO: Instead of dropping off parity, check parity and if error clear CardRead and CardWordH/L
'Even Parity: LSB should be 0
'Odd  Parity: LSB should be 1
                CardWordL = CardWordL >> 1 'Drop odd parity
                CardWordL.15 = CardWordH.0 'CardWordL contains full user code
                CardWordH.9 = 0 'Drop even parity
                CardWordH = CardWordH >> 1 'We copied this bit to CardWordL already so drop it
                CardRead = 1
        EndIf
Return
'''''''''''''''''''''''''''''''
''' LCD subroutines below
'''''''''''''''''''''''''''''''
LCD_init:
        PORTD = %00000001 'clr screen
        GoSub lcd_cmd
        portd = %00111000 '8 bits 2 lines 5*7 mode.
        GoSub lcd_cmd
        portd = %00001101 'display on, cursor off, blink on.
        GoSub lcd_cmd
        portd = %00000110 'no shift, cursor move right.
        GoSub lcd_cmd
        portd = %10000000 'set ddram address?
        GoSub lcd_cmd
return

write_splash:
        PORTD = %00000001 'clr screen
        GoSub lcd_cmd
        For i = 0 to 15
                LOOKUP i, ["RFID CONTROLLER "], x
                GoSub lcd_data
        Next i
        PORTD = %11000000 'set the 2nd line display address
        GoSub lcd_cmd
        For i = 0 to 15
                LOOKUP i, ["(C) TONY FULLER "], x
                GoSub lcd_data
        Next i
        Pause 1000
return

lcd_data:
        PORTD = x 'Set up PORTD[0:7] with correct outputs from temp variable
        rs = 1 'Data
        rw = 0 'Write mode
        e = 0 'make enable port low
        Pause 10
        e = 1 'now create edge
return

lcd_cmd:
        rs = 0 'Command
        rw = 0 'Write mode
        e = 0 'make enable port low
        Pause 10
        e = 1 'now create edge
return

'''''''''''''''''''''''''''''''
''' That's all folks
'''''''''''''''''''''''''''''''
end

---

One note about the EEPROM data is that the site code is not stored, it's in a separate constant. The stored data is actually backwards: The first entry is 33971 in hex that is 84B3 so in the EEPROM data it is stored as B3 84. It becomes easier to read that way in the for loop.