ds1820 error

[CrazyCooter]

i have tried it without the READ POWER SUPPLY. I have also tied a 4.7k resistor from the DQ line to 5V. Am i initialising it correctly??? This was a direct copy from melabs using "onewire.bas"

[james]

Did you set internal osc?

Right after you compile, the screen comes up to program the chip. if you click view -> configuration. You can set INTOSC.

a place I've tripped up before, just a thought.

hope it helps

[Bruce]

Try changing this;
OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

to this;
OWIn DQ, 2, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

I beleive you need mode 2 after the last read to issue the reset pulse so the sensor
is ready for the next on return to the start of your program.

[Darrel Taylor]

I had to try it out, but all I have is a DS18B20.

The original code worked fine, except I had to change the formula. But the communications seems OK.
<br>

[CrazyCooter]

ok have got it to work. i replaced the 4k7 resistor with a 2k4 resistor and rererererereread the data sheet for the ds1820 and put a pause 750 after the start temp conversion. IE.
OWOUT DQ,1, [$CC, $44]
PAUSE 750 ' Max conversion time
OWIN DQ, 4, [count_remain]

i found it on pg 20 under AC Electrical Characteristics temperature conversion time

i found its not as fast as i would have thought. is there any other way to make it faster or is this the speed of using the 1 wire devices

the code

OSCCON = %01101000 'INTRC = 4 MHz
TRISA = %11111111
ANSEL = 0 'DISABLE ALL ADC
CMCON = 7 'DISABLE ALL ANALOG COMPARATOR
WHILE OSCCON.2=0:WEND 'STABILISE THE CLOCK
ADCON1 = 1
DEFINE OSC 4
PAUSE 1000
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT 4 '4,5,6,7
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 3
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 2
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2
DEFINE LCD_COMMANDUS 2000
DEFINE LCD_DATAUS 50
pause 1000
lcdout $fe, 1

' One-wire temperature for DS18S20

' This program must be compiled with PBP version 2.40 or later


temperature VAR WORD ' Temperature storage
count_remain VAR BYTE ' Count remaining
count_per_c VAR BYTE ' Count per degree C

DQ VAR PORTA.1 ' One-wire data pin

mainloop:
OWOut DQ, 1, [$CC, $44] ' Start temperature conversion
pause 750 'NEEDED FOR TEMP STABILIZING
waitloop: OWIn DQ, 4, [count_remain] ' Check for still busy converting
IF count_remain = 0 Then waitloop

OWOut DQ, 1, [$CC, $BE] ' Read the temperature
OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

' Calculate temperature in degrees C to 2 decimal places (not valid for negative temperature)
temperature = (((temperature >> 1) * 100) - 25) + (((count_per_c - count_remain) * 100) / count_per_c)
LCDOut $fe, 1, DEC (temperature / 100)," C"

GoTo mainloop ' Do it forever
end

thanks

crazy cooter

[Darrel Taylor]

Hmmm, something doesn't seem right.

The lower value pull-up, and pause 750 shouldn't be needed.
The OWIn DQ, 4, [count_remain] will check the busy bit until the conversion is complete.

..... Unless it's running on "Parasite Power". In which case you need a Strong Pull-up on DQ during the conversion, and you can't read from the device for 750ms.

If that fixed your problem, then you probably don't have 5V on pin 3 of the 1820.
And if "Parasite Power" was intentional, you may need to do things differently.
<br>

[CrazyCooter]

Hi everyone
Well this ds1820 ic is being a real pain. have gone over things with a multimeter and i have 5v going to pin 3. data is pin 2 and gnd is pin 1

This is what the front of the ic looks
________
dallas
ds1820
0634C3
+552AC
________
1 2 3
GND 5V
DATA
2k4 resistor tied between pin 2 and pin 3

I did notice "Vpu" figure 1 page 2 of the data sheet. What is Vpu is that the 5v line as i am using it. I assume it is. Could this be the problem??

Am BALD cause of this ic. hahaha