DS1820 and 18f2550

[Acetronics2]

Hi, Rich

I have a DS1820 "on board" ... I look at that.

Here is an excerpt of my test program:



'************************************************* ****************************
' Start temperature conversion
'************************************************* ****************************

mainloop: OWOut DQ, 1, [$CC, $44 ]

'************************************************* ****************************
' Check for still busy converting ( ~ 4500 times ... )
'************************************************* ****************************

waitloop:

INPUT DQ
If NOT DQ Then waitloop

'************************************************* ****************************
' Read the temperature
'************************************************* ****************************

OWOut DQ, 1, [$CC, $BE ]

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)+ offset

Lcdout $fe, 1, DEC (temperature / 100), ".", DEC2 temperature, " ",$DF,"C"

'************************************************* ****************************
' Calculate temperature in degrees F to 2 decimal places (not valid for negative temperature)
'************************************************* ****************************

temperature = (temperature */ 461) + 3200
Lcdout $fe, $c0, DEC (temperature / 100), ".", DEC2 temperature, " ",$DF,"F"






the major thing is see is here :

OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

as you receive more than 16 bits ... and your "buffer" is only 16 bits.

The Scratchpad is always FULLY read ( 8 bytes ), so you must skip the last locations.

see datasheet on page 8 for scratchpad details.

Alain