CCITT CRC16 [CRC-16] Routines

'*********************************************************************
'*  Name    : CRC16.BAS                                [CCITT CRC16] *
'*  Author  : Ashley Roll, Phil Ciebiera                             *
'*  Notice  : Derived from works at:                                 *
'*          : www.digitalnemesis.com/info/codesamples/embeddedcrc16/ * 
'*          : Ported to Proton+ BASIC - www.protonbasic.co.uk/       *
'*  Date    : 2/21/2011                                              *
'*  Version : 1.0                                                    *
'*  Notes   : Test Vector: 0x313233343536373839 : 0x29B1             *
'*          : Test Vector: 0x393837363534333231 : 0x84DF             *
'*          : Continuously calculates CRC16 CCITT on incoming USART1 *
'*          : PIC®18F46K22 INTOSC 16x4PLL 64MHz - Connect 9600 8-N-1 *
'*          : This code is shared under The MIT License              *
'*********************************************************************


'--- BEGIN: Microchip™ PIC® INITIALIZATION ---
Device 18F46K22
Xtal 16
All_Digital True

Config_Start
    FOSC = INTIO67  ' Internal oscillator block, port function on RA6 and RA7
    PLLCFG = On     ' Oscillator multiplied by 4  
    PRICLKEN = On   ' Primary clock is always enabled
    FCMEN = Off     ' Fail-Safe Clock Monitor disabled
    IESO = Off      ' Oscillator Switchover mode disabled
    PWRTEN = Off    ' Power up timer disabled
    BOREN = Off     ' Brown-out Reset disabled in hardware and software
    WDTEN = Off     ' Watch dog timer is always disabled. SWDTEN has no effect.
    'WDTPS = 1      ' 1:1
    CCP2MX = PORTB3 ' CCP2 input/output is multiplexed with RB3
    PBADEN = Off    ' PORTB<5:0> pins are configured as digital I/O on Reset 
    CCP3MX = PORTB5 ' P3A/CCP3 input/output is multiplexed with RB5  
    HFOFST = On     ' HFINTOSC output and ready status are not delayed by the oscillator stable status
    T3CMX = PORTC0  ' T3CKI is on RC0
    P2BMX = PORTD2  ' P2B is on RD2
    MCLRE = EXTMCLR ' RE3 input pin enabled; MCLR disabled
    STVREN = Off    ' Stack full/underflow will not cause Reset
    LVP = On        ' Single-Supply ICSP disabled
    XINST = Off     ' Instruction set extension and Indexed Addressing mode enabled
    Debug = Off     ' Disabled
    CP0 = Off       ' Block 0 (000800-003FFFh) not code-protected  
    CP1 = Off       ' Block 1 (004000-007FFFh) not code-protected
    CP2 = Off       ' Block 2 (008000-00BFFFh) not code-protected  
    CP3 = Off       ' Block 3 (00C000-00FFFFh) not code-protected
    CPB = Off       ' Boot block (000000-0007FFh) not code-protected
    CPD = Off       ' Data EEPROM not code-protected  
    WRT0 = Off      ' Block 0 (000800-003FFFh) not write-protected
    WRT1 = Off      ' Block 1 (004000-007FFFh) not write-protected  
    WRT2 = Off      ' Block 2 (008000-00BFFFh) not write-protected  
    WRT3 = Off      ' Block 3 (00C000-00FFFFh) not write-protected
    WRTC = Off      ' Configuration registers (300000-3000FFh) not write-protected  
    WRTB = Off      ' Boot Block (000000-0007FFh) not write-protected
    WRTD = Off      ' Data EEPROM not write-protected  
    EBTR0 = Off     ' Block 0 (000800-003FFFh) not protected from table reads executed in other blocks
    EBTR1 = Off     ' Block 1 (004000-007FFFh) not protected from table reads executed in other blocks  
    EBTR2 = Off     ' Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks  
    EBTR3 = Off     ' Block 3 (00C000-00FFFFh) not protected from table reads executed in other blocks
    EBTRB = Off     ' Boot Block (000000-0007FFh) not protected from table reads executed in other blocks  
Config_End 

OSCCON.4 = 1 
OSCCON.5 = 1 'FOR 16MHZ
OSCCON.6 = 1 

DelayMS 300
'--- END: Microchip™ PIC® INITIALIZATION ---

' Jump over CRC16 Definitions to the Demo
GoTo DemoStart

' --- BEGIN: CRC16 RELATED ---
' CRC16 Result Bytes
Dim bCRC16_High As Byte
Dim bCRC16_Low As Byte
' Internal Work Variables
Dim bCRC16_Work1 As Byte
Dim bCRC16_Work2 As Byte
' CRC16 I/O Bytes
Dim bCRC16_Input As Byte
Dim wCRC16_Output As Word

' Sets the initial CRC value
CRC16_Initialize:
    bCRC16_High = $FF
    bCRC16_Low = $FF
Return

' Processes the CRC16 from the byte at bCRC16_Input and updates the checksum at wCRC16_Output
CRC16_ProcessInput:    
    ' process byte from CRC16_Input
    ' High Nibble
    bCRC16_Work2 = bCRC16_Input >> 4
    GoSub CRC16_ProcessNibble
    ' Low Nibble
    bCRC16_Work2 = bCRC16_Input & $0F
    GoSub CRC16_ProcessNibble
    ' Assemble output word
    wCRC16_Output.LowByte = bCRC16_Low
    wCRC16_Output.HighByte = bCRC16_High
Return

' Actually computes a 4-bit CRC
CRC16_ProcessNibble:
    ' Step one, extract the Most significant 4 bits of the CRC register
    bCRC16_Work1 = bCRC16_High >> 4
    ' XOR in the Message Data into the extracted bits
    bCRC16_Work1 = bCRC16_Work1 ^ bCRC16_Work2  
    ' Shift the CRC Register left 4 bits
    bCRC16_Work2 = bCRC16_Low >> 4
    bCRC16_High = bCRC16_High << 4
    bCRC16_High = bCRC16_High | bCRC16_Work2
    bCRC16_Low = bCRC16_Low << 4
    ' Do the table lookups and XOR the result into the CRC Tables
    ' High byte
    bCRC16_Work2 = CRead (CRC16_LookupTables + bCRC16_Work1)
    bCRC16_High = bCRC16_High ^ bCRC16_Work2
    ' Low byte
    bCRC16_Work2 = CRead (CRC16_LookupTables + 16 + bCRC16_Work1)
    bCRC16_Low = bCRC16_Low ^ bCRC16_Work2
Return
' --- PAUSE: CRC16 RELATED ---

 
' --- BEGIN: DEMO RELATED ---
DemoStart:
;Calculated Baudrate = 9592 @ Xtal 16MHz, Error = -0.08%
RCSTA     = 144 ; Enable continuous receive
TXSTA     = 36  ; Enable transmit, BRGH = 1
SPBRG     = 160 ; Baud Rate Generator Low Byte Value
SPBRGH    = 1   ; Baud Rate Generator High Byte Value
BAUDCON.3 = 1   ; Enable the 16 bit Baud Rate Generator
Declare Hserial_Clear On
Dim ser_data As Byte
GoSub CRC16_Initialize
Demo:
    HSerIn 100, Demo, [ser_data]    ' Listen for a byte on the USART
    bCRC16_Input = ser_data         ' Assign the byte to the CRC16 routine input
    GoSub CRC16_ProcessInput        ' Process the CRC16 for the byte
    HSerOut [ser_data,": ",Hex4 wCRC16_Output,13,10] ' Output the formatted result
GoTo Demo                           ' Loop
' --- END: DEMO RELATED ---

   
' --- RESUME: CRC16 RELATED ---
' CRC16 computational lookup tables
CRC16_LookupTables:
CData $00, $10, $20, $30, $40, $50, $60, $70, $81, $91, $A1, $B1, $C1, $D1, $E1, $F1    ' CRC16_Lookup High
CData $00, $21, $42, $63, $84, $A5, $C6, $E7, $08, $29, $4A, $6B, $8C, $AD, $CE, $EF    ' CRC16_Lookup Low
' --- END: CRC16 RELATED ---