Pull-ups on 16F88

[Steves]

Hi Tenaja,here is my code for the A/D part of my project. I have tried it and find that accuracy is better the further away from 0V the input voltage is.

INCLUDE "modedefs.bas"

@ DEVICE pic16F88, INTRC_OSC_NOCLKOUT ' system clock options
SI VAR PORTB.1 ' Serial output pin
SO VAR PORTB.2 ' Serial Input pin
dig_num var word
x var word
num var word
remain var word

TRISA = %00000001 'bit 0 (AN/0) is input
TRISB = %10000010 'bit 7 (AN6) is input bit 1 is serial in
OSCCON = %01101000 '4MHz clock
ANSEL = %01000001 'AN0 and AN6 are analog
ADCON0 = %11110001 'channel 6 is selected
ADCON1 = %01000000 'Ref is Vdd and Vss
OPTION_REG.7=1 'dissable weak pull-ups on portB?
pause 2000 'let power supply settle
sens_in:
serout2 SO,813,["Hello",13,10] 'test serial connection
'see if all registers are set OK
serout2 SO,813,["ADCON0 = ",#ADCON0,13,10]
serout2 SO,813,["ADCON1 = ",#ADCON1,13,10]
serout2 SO,813,["ANSEL = ",#ANSEL,13,10]
serout2 SO,813,["OSCCON = ",#OSCCON,13,10]
serout2 SO,813,["OPTION_REG = ",#OPTION_REG,13,10]
serout2 SO,813,["Before A/D in",13,10]
'check digital value of A/D before conversion
serout2 SO,813,["Digital num = ",#dig_num,13,10]
pause 5000

ADCIN 6, dig_num 'use chanel 6 (RB7/AN6) as A/D input dig_num is digital result
while ADCON0.2=1:WEND ' Check to make sure ADC conversion finished..
pause 250

serout2 SO,813,["After A/D in",13,10] 'let meknow A/D is finished
x = dig_num*39
num = x/1000
remain = (x//1000)/100
serout2 SO,813,["dig_num = ",#dig_num,13,10]
serout2 SO,813,["x = ",#x,13,10]
serout2 SO,813,["Result = ",#num,".",#remain,13,10]

pause 5000

goto sens_in
end

An open input results in a 10V reading. I have looked thru the D/S again as you suggested, but cannot find any ref. to internal pull-ups other than setting OPTION_REG.7, though measurement indicates that they exist.
Sometimes though you see what you expect to and my reg. settings may well be wrong.
Thanks for the help
Steve

[Archangel]

Hi Steve,
Your config statement has noclockout option for osc, you might try INTRC_OSC, I am not too familiar with the PM assembler, in MPASM it says _INTRC_IO, and does not offer a NO_CLKOUT for this chip. Also the FCMEN_OFF should be in there as Device 2 as it is hooked up to the port you are using, put a scope on that port you might see a 32kc signal there . . . maybe.
the following is from the pm assembler's file about this chip:

					; *** DEVICE Device Definitions
PIC16F88	equ     50081003h       ; 14-Bit, 4K Code, 256 EE, ID = 3

					; *** DEVICE Fuses Definitions
EXTRC_OSC_CLKOUT equ    3FEC0013h       ; XX XXXX XXX1 XX11
EXTRC_OSC_NOCLKOUT equ  3FEC0012h       ; XX XXXX XXX1 XX10
EXTRC_OSC       equ     3FEC0012h       ; XX XXXX XXX1 XX10
INTRC_OSC_CLKOUT equ    3FEC0011h       ; XX XXXX XXX1 XX01
INTRC_OSC_NOCLKOUT equ  3FEC0010h       ; XX XXXX XXX1 XX00
INTRC_OSC       equ     3FEC0010h       ; XX XXXX XXX1 XX00
EXTCLK_OSC      equ     3FEC0003h       ; XX XXXX XXX0 XX11
EC_OSC          equ     3FEC0003h       ; XX XXXX XXX0 XX11
HS_OSC          equ     3FEC0002h       ; XX XXXX XXX0 XX10
XT_OSC          equ     3FEC0001h       ; XX XXXX XXX0 XX01
LP_OSC          equ     3FEC0000h       ; XX XXXX XXX0 XX00
WDT_ON          equ     3FFB0004h       ; XX XXXX XXXX X1XX
WDT_OFF         equ     3FFB0000h       ; XX XXXX XXXX X0XX
PWRT_ON         equ     3FF70000h       ; XX XXXX XXXX 0XXX
PWRT_OFF        equ     3FF70008h       ; XX XXXX XXXX 1XXX
MCLR_ON         equ     3FDF0020h       ; XX XXXX XX1X XXXX
MCLR_OFF        equ     3FDF0000h       ; XX XXXX XX0X XXXX
BOD_ON          equ     3FBF0040h       ; XX XXXX X1XX XXXX
BOD_OFF         equ     3FBF0000h       ; XX XXXX X0XX XXXX
LVP_ON          equ     3F7F0080h       ; XX XXXX 1XXX XXXX
LVP_OFF         equ     3F7F0000h       ; XX XXXX 0XXX XXXX
CPD_ON          equ     3EFF0000h       ; XX XXX0 XXXX XXXX
CPD_OFF         equ     3EFF0100h       ; XX XXX1 XXXX XXXX
WRT_1FOURTH     equ     39FF0000h       ; XX X00X XXXX XXXX
WRT_HALF        equ     39FF0200h       ; XX X01X XXXX XXXX
WRT_3FOURTHS    equ     39FF0400h       ; XX X10X XXXX XXXX
WRT_OFF         equ     39FF0600h       ; XX X11X XXXX XXXX
DEBUG_ON        equ     37FF0000h       ; XX 0XXX XXXX XXXX
DEBUG_OFF       equ     37FF0800h       ; XX 1XXX XXXX XXXX
CCPMX_ON        equ     2FFF0000h       ; X0 XXXX XXXX XXXX
CCPMX_OFF       equ     2FFF1000h       ; X1 XXXX XXXX XXXX
PROTECT_ON      equ     1FFF0000h       ; 0X XXXX XXXX XXXX
PROTECT_OFF     equ     1FFF2000h       ; 1X XXXX XXXX XXXX

					; *** DEVICE2 Fuses Definitions
FCMEN_OFF	equ     3FFE0000h       ; XX XXXX XXXX XXX0
FCMEN_ON	equ     3FFE0001h       ; XX XXXX XXXX XXX1
IESO_OFF	equ     3FFD0000h       ; XX XXXX XXXX XX0X
IESO_ON		equ     3FFD0002h       ; XX XXXX XXXX XX1X