A/D conversion problem on 18F4431
Hi,
Ver 2.46, MPMASM 5.1
I have the processor above with an analog accelerometer. The values I'm getting from the conversion are incorrect with respect to the reference voltage supplied. I have tried numerous configuration changes but no luck.
Setup:
Ref+ voltage is 2.6v on Pin RA3,
Ref- is Gnd.
measured voltages
RA0 = x-dir 1.1v
RA1 = y-dir .9v
RA2 = z-dir 1.8v
Acc. value 1g=800mV/g.
I was expecting to see the voltages for x and y to be ~1.3 volts or a value displayed of ~ 512 when the acc. is in the horizontal position. What I get now are reading of 900-1000. I tested this on an 16F877A and it preformed as expected. Also, I tried all 1.5, 2, 4, 6 g settings. No change.
Code is below:
DEFINE OSC 8
OSCCON = %01110010
'
' Define LCD pins
'
DEFINE LCD_DREG PORTD 'LCD data port
DEFINE LCD_DBIT 4 'LCD data starting bit 0 or 4
DEFINE LCD_BITS 4 'LCD bus size 4 or 8
DEFINE LCD_RSREG PORTC 'LCD register select port
DEFINE LCD_RSBIT 1 'LCD register select bit
DEFINE LCD_RWREG PORTC 'LCD read/write port
DEFINE LCD_RWBIT 2 'LCD read/write bit
DEFINE LCD_EREG PORTC 'LCD enable port
DEFINE LCD_EBIT 3 'LCD enable bit
wAdval var word
bLoop var byte
wMaxvalArray var word[3]
wMinvalArray var word[3]
m var byte
'I/O port defs 0=out, 1=in
' atod
TRISA = %00001111 ' AI 0=x-dir, AI 1=y-dir, 2=nc, AI 3=z-dir
' DO 4=g1, DO 5=g2, DO 6=nc, DO 7=nc
PORTA = 0
TRISB = %11111111 ' DI 0=sel, DI 1=up, DI 2=dn, DI 3=end
' DI 4=nc, DI 5=LVPGM, DI 6=PGC, DI 7=PGD
PORTB = 0 ' PORTB lines low to read buttons
TRISC = %00000000 ' All DO's 3 LCD, 4=cont, 5=LCD_RW, 6=LCD_RS, 7=LCD_E
PORTC = 0 ' PORTC lines low to read buttons
TRISD = %00000000 ' not used
PORTD = 0
TRISE = %00001000 ' DI 0=sleep, DO 1=nc, DO 2=nc, DI 3=MCLR
PORTE = 0
' port assignments
aACC_g1 var PortA.5
aACC_g2 var PortE.0
aACC_SLEEP var PortA.4
ANSEL0 = %00000111 ' set 0,1,2 to AI, rest to Digital
ANSEL1 = %00000000 ' set 0 to Digital, rest are n.c.
INTCON = %00000000
INTCON2 = %00000000
INTCON3 = %00000000
ADCON0 = %00000000 ' sin. shot meas, multichan, sim M1, DONE, a/d mod OFF
ADCON1 = %01011000 ' Vdd-ACC volt, Vss refs, FIFO en, buffer stuff
ADCON2 = %10000011 ' rt just., No conv delay, FRC/4
ADCON3 = %11000000 ' int. unimpl, all trigs. disabled
ADCHS = %01000000 ' group sel., Group D=AN3, Group B=AN1, Group A=AN0
' wake acc.
aACC_SLEEP = 1
' 1.5 g
aACC_g1 = 0'01
aACC_g2 = 0'01
ADCON0.0 = 1 'a/d mod ON
m = 0
wMinvalArray[m+1] = 1024
wMaxvalArray[m+1] = 0
wMinvalArray[m+2] = 1024
wMaxvalArray[m+2] = 0
wMinvalArray[m+3] = 1024
wMaxvalArray[m+3] = 0
'////////////////////////////////
'
' mainloop - the mother of all
'
'////////////////////////////////
mainloop:
for m = 1 to 3
if m = 1 then ADCON0 = %00000001
if m = 2 then ADCON0 = %00000101
if m = 3 then ADCON0 = %00001001
ADCON0.1 = 1 ' Start Conversion
Pause 5
notdone:
If ADCON0.1 = 1 Then goto notdone
Pause 5
' good conversion, grab the data
wAdval.LowByte = ADRESL
wAdval.HighByte = ADRESH
if wAdval < wMinvalArray[m] then wMinvalArray[m] = wAdval
if wAdval > wMaxvalArray[m] then wMaxvalArray[m] = wAdval
next m
lcdout $fe, $1, "x", Dec4 wMinvalArray[1], "-", DEC4 wMaxvalArray[1], _
"y", Dec4 wMinvalArray[2]
lcdout $fe, $c0, "-", DEC4 wMaxvalArray[2], _
" z", Dec4 wMinvalArray[3], "-", DEC4 wMaxvalArray[3]
Goto mainloop ' Do it forever
