list p=18f452
    include "p18f452.inc"


    variable databit
    databit set b'000000000'
    potused set b'000000000'
    totalresmul set d'0'

     UDATA_ACS
    DN  res	1
    RA  res	1   ;Wiper A
    RB  res	1   ;Wiper B
    RAB  res	2   ;Total Res

     ; Declare a code section at 0x0 named 'RST'. This instruction sends the
    ; program to the actual start of the program.
RST code    0x0000
    GOTO    Setup

    ; Declare a code section at 0x0030. This is where the actual program logic will start
SRT code    0x0060




Setup:
    totalres = 720
    ;Load the Total Res into an easier to locate ram loco
    MOVLW   HIGH totalres   ;We dont worry about full number, it is divided by 256
    MOVWF   RAB
    RLNCF		    ;Save first two bits /256 = first two bits+1
    RLNCF
    MOVLW   b'11'
    ANDWF   RAB
    MOVLW   b'1'
    ADDWF   RAB		    ;Total Resistance has been setup

    call SetupPortB
    call SetupSPI
    potused = b'10'
    databit = d'86' ;Set N a percentage of the Pot Value
    call convertN   ;The argument N is now placed in W before the subroutine is called
    call VSetPotBW


;Converts N a percentage to a 255 bit number
convertN:
    MOVLW databit
    MULLW 0xFF		; percentage * 255 = 16 bit number. First 8 bits are the new number
    MOVFF PRODH, W	;Move the high byte of the multiplication to the W


VSetPotBW:
    ;Sets the resistance between B and W (wiper to N% of the potentionmeters value)
    MOVWF   DN    ;Store the value W in a better location
    potused = b'01' ;Set the Wiper A first
    selectP
    databit = DN
    call WriteToP
    potused = b'10'
    selectP
    databit = DN
    call WriteToP

SetupPortB:
    BCF	PORTB, 3
    BSF	TRISB,	3   ;
    RETURN

SetupSPI:
    BSF	SSPSTAT, CKE
    BCF	SSPSTAT, SMP	;Sampled in the middle
    BSF	SSPCON1, SSPEN	;Enables SCK, SDO, SDI and SS
    MOVWF b'0001'	;Set the SPI Master mode to FOSC/16 (Pot works on 16)
    IORWF SSPCON1


    BSF TRISC, 4	;Serial Data In (SDI) - Connected to
    BCF TRISC, 3	;Serial Clock (SCK)
    BCF TRISC, 5	;Serial Data Out (SDO)
    RETURN

selectP:
    BCF	PORTB, 3	;Set CS to LOW
    MOVLW b'00100000' ;Set to shutdown for selection
    MOVWF SSPBUF    ;Send First byte (the command byte)
    BSF	PORTB, 3
    call WaitforSSPConversion
    BCF	PORTB, 3	;Set CS to LOW
    MOVWF potused	;Selects Pot
    IORWF SSPBUF
    BSF	PORTB, 3

WriteToP:
    ;SETTING UP THE COMMAND BYTE
    BCF	PORTB, 3	;Set CS to LOW
    ;Write in Values
    MOVLW b'00010000' ;Turn on the write byte, Select Potentiometer
    MOVWF SSPBUF    ;Send First byte (the command byte)

    BSF	PORTB, 3	;Set CS to High to execute the command
    call WaitforSSPConversion

    ;SETTING UP THE DATA BYTE
    BCF	PORTB, 3	;Set CS to LOW
    MOVLW databit	;The Data Byte is created
    MOVWF SSPBUF	;Send the data to the Pot
    BSF	PORTB, 3	;Set CS to High to execute the command
    call WaitforSSPConversion
    RETURN



WaitforSSPConversion:
    btfss   SSPSTAT, BF      ; Wait for the Buffer to become full
    goto    WaitforSSPConversion
    RETURN


    ;Set CS Low
    ;clocking in a command byte and then a data byte into the 16 bit shift regist
    ;;Executed when CS is raised
    ;Clocked in on the rising edge of the clock andf out the SO pin on the falling edge
    ;Command Byte - two command select bytes and two potenitometer select bits
    ;c1 and c0 (bits 4 and 5) - 01 write command will be executed to the 8 bits
    ; 10 shutdown


   ; SSPBUF = 0xFF;              // Sends data in order to read from the buffer
       ;     while ( !SSPSTATbits.BF );  // wait until cycle complete
    ;

    end