>
> Last night insomnia set in, and I was thinking about all the really obscure
> factoids you have to keep in mind to use a PIC.  These are the things that
> newbies get stumped on, and end by gnashing their teeth, rending their
> clothes, and pulling out their hair.  That's why most PIC experts are bald.
> (;-)  I wondered if List Members could add enough obscure factoids to reach
> 100?  Most of us know these by heart, through long arduous trial and error,
> and never think about them twice anymore.
>

Ok, I have one for you. Maybe the list could explain to me (1 year newbie)
why this one didn't work. Maybe it has (or will) bitten someone else before.
I was trying the "light the LEDS to = the A2D voltage" exercise
I'm sure most go through. When I started the A2D conversion, the way
I readit, the A2D needs a minimum aquisition time, that one
needs to calculate depeding on the clock freq. and how you assign
it etc. Looking at the examples, it seemed that with a 4 mhz clock,
it would need at least a dozen usecs or so. Since this was just
an exercise, I figured I'd give it plenty of time (2 msecs)
to do the aquisition. So after starting up the conversion, I called
my delay routine, and then tried to read and display the ref in binary
on the LEDS. The offending lines are in the code below where the
comment has a big NO!!. Once I commented out those two lines the
code started "working". (i.e. I had to complement the results of
the A2D to get the right LEDS to light :-) ). Took me 5 days of
pain to figure this one out, since the Simulator didn't show it.
Sorry for the rather long post. Any general code comments (e.g. style or
efficiency, reuseability, etc.) are welcome.

Steve
;                                                                     *
;    Filename:      a2d2.asm                                          *
;    Date: Wed Jul 25 13:48:42 CDT 2001                               *
;    Author: -sm.                                                     *
;**********************************************************************
;#DEFINE DEBUG

        list      p=16c716            ; list directive to define processor
        #include "p16c716.inc"        ; processor specific variable definitions

        __CONFIG   _CP_OFF & _WDT_OFF & _BODEN_ON & _PWRTE_ON & _HS_OSC

        ;errorlevel  -302              ; suppress message 302 from list file

;***** VARIABLE DEFINITIONS
loop_cnt equ    0x20    ; Delay Counter (times thru delay loops)
delay_1  equ    loop_cnt +1     ; loop 1
delay_2  equ    loop_cnt +2     ; loop 2
delay_3  equ    loop_cnt +3     ; loop 3
delay_4  equ    loop_cnt +4     ; loop 4
results  equ    loop_cnt +5     ; sent to LEDS

;**********************************************************************
                ORG     0x000
                goto    main              ; go to beginning of program

main
                bsf     STATUS,RP0        ; set file register bank to 1

                clrf    PORTA
                movlw   b'00000010'  ; RA1 (pin 18)input, others outputs port A
                movwf   TRISA;

                clrf    PORTB
                movlw   b'00000000'     ; Port B all outputs
                movwf   TRISB;

                bcf     INTCON, GIE ; Don't bug me-all interuppts disabled

                movlw   b'00000000' ; port A analog inputs Vref internal = Vdd
                movwf   ADCON1

                bcf     STATUS,RP0        ; set file register bank to 0

                movlw   b'11001001' ; clock int osc, AN1 selected, a2d on
                movwf   ADCON0
                clrf    ADRES
                clrf PORTB  ; LEDS on
                movlw 0xfa
                call delay
begin
                movlw 0xff
                movwf PORTB  ; LEDS off
                movlw 0xff      ; a little delay to catch leds
                call delay
                bsf ADCON0, GO    ; start the A2D conversion
; BUG or anomaly next two lines
                ;movlw 0x02     ; give a2d some time to aquire (~2 msec) NO!!!
                ;call delay
testbit
                btfss ADCON0, NOT_DONE
                goto testbit
                          ; a2d complete done flag is cleared
                movf ADRES, w
                movwf results
                comf  results, 1  ;Change 1 to 0s for lighting LEDS
                movf results, w
                movwf   PORTB
                movlw 0xfa
                call delay
                goto    begin

;**********************************************************************
; delay.asm
; with clock at 4 Mhz
; with loop_cnt = 0a, delay_X = 1       time = 165usecs
; with loop_cnt = 0a, delay_X = ff      time = 30.64msecs
; with loop_cnt = 3a, delay_X = ff      time = 177.7smsecs
; with loop_cnt = 4a, delay_X = ff      time = 226.74msecs
; with loop_cnt = 4a, delay_X = f0      time = 213.42msecs
; with loop_cnt = 4a, delay_X = fe      time = 224.97msecs
;                                                                     *
;**********************************************************************


delay

        IFDEF DEBUG
                movlw   0x01    ;
        ENDIF
        movwf   loop_cnt

delay_loop

        IFDEF DEBUG
                movlw   0x02    ;
        ELSE
                movlw   0xfd    ;
        ENDIF

        movwf   delay_1
        movwf   delay_2
        movwf   delay_3
        movwf   delay_4

dlay1
        decfsz  delay_1, 1
        goto    dlay1
dlay2
        decfsz  delay_2, 1
        goto    dlay2
dlay3
        decfsz  delay_3, 1
        goto    dlay3
dlay4
        decfsz  delay_4, 1
        goto    dlay4
        decfsz  loop_cnt, 1
        goto    delay_loop

        return

        END                       ; directive 'end of program'

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