; pot.asm

; Program to demonstrate getting data via the AD converter attached to the 5K potentiometer
; on the Raven board.  The 5K pot is connected to RE0 which is one of the AD converters on the
; 16F877.  The diagram is (sort of):
;
;             Vcc
;              |
;              |            |---- RE0
;              <            |
;         5K   < <----vvv---|
;              <      100
;              |
;              Vdd

;The input to the pot is 5 volts, which is then fed through the pot which has resistance varying
; from 0 to 5000 ohms and then through the 100 ohm (R11) resistor.  So the voltage seen at RE0 will
; vary from 
;


        LIST P=16F877, R=DEC

        INCLUDE "P16F877.inc"

; Definitions

;  __CONFIG _CP_OFF & _DEBUG_OFF & _WRT_ENABLE_OFF & _CPD_OFF & _LVP_OFF & _BODEN_OFF & _PWRTE_ON & _WDT_OFF & _HS_OSC20

; Define start of vars

RAM        EQU   0x20

; Variables

Temp       EQU   RAM+0
ADValHi    EQU   RAM+1
ADValLo    EQU   RAM+2
DTemp1     EQU   RAM+3
DTemp2     EQU   RAM+4

; Start of the Program

        ORG       3
        goto      Start


        ORG       0x20
Start

        bsf       STATUS, RP0
        clrf      TRISA                      ; for output of value to led bar
        clrf      TRISD
        bsf       TRISE,0                    ; input port
        bcf       STATUS, RP0

        call      ADConfig

; This loop starts the AD conversion process and then keep getting values and outputting to 
; the led_bar

        bsf       ADCON0,GO                  ; start the conversion

main_loop
        call      ADConvert
        iorlw     0
        btfss     STATUS,Z
        goto      main_loop

; Output the current value - first low and then hi with 250 ms delay

        movf      ADValLo,W
        call      DispLedBar
        movlw     250
        call      Delay_ms

        movf      ADValHi,W
        call      DispLedBar

; half second delay after second byte
     
        movlw     250
        call      Delay_ms
        movlw     250
        call      Delay_ms

        goto      main_loop
             
; -------------------------------------------------------------------
; AD routines

ADConfig
; Set the conversion clock rate to Fosc/32, enable RE0 and turn on A/D conversion

        movlw      b'10101001'
        movwf      ADCON0

; Configure the pin behavior, right justified, Vref+=Vdd, Vref-=Vss

        bsf        STATUS,RP0
        movlw      b'10001001'
        bcf        STATUS,RP0

        return

ADConvert

; Check to see if the conversion is done.

        btfss      ADCON0, GO
        goto       convert_done

; Return W = 0 to show that it is not complete

        retlw      0

convert_done        
; Yes, get the value and store it.
; 
        bsf        STATUS, RP0
        movf       ADRESL, W
        bcf        STATUS, RP0
        movwf      ADValLo
        movf       ADRESH, W
        movwf      ADValHi

; So now, start another conversion

        bsf        ADCON0, GO

; Return W = 1 to show that it is complete

        retlw      1


        return

; -----------------------------------------------
; Output a value to the LED bar

DispLedBar

; Enable the led bar and put the value in W there.

        movwf     Temp             ; save W
        movlw     0x12
        movwf     PORTA

        comf      Temp,W
        movwf     PORTD

        return

; -------------------------
; Delay milliseconds

Delay_ms
        bsf     STATUS,RP0
        bsf     STATUS,RP1

        movwf  	DTemp1
dloop_0	                ; number of ms to delay
        movlw  	250
        movwf  	DTemp2
dloop_1	                ; 1 ms delay (approximately)
        fill (nop), 17
        decfsz 	DTemp2,F
        goto    dloop_1
        decfsz 	DTemp1,F
        goto   	dloop_0

        bcf     STATUS,RP1
        bcf     STATUS,RP0
        return

        END