' =========================================================================================
'
' Program: DS1821HI.BAS
' Author: Dusko Djuricin
' E-mail: djdusko@eunet.yu
'
' This program demonstrates how to increase resolution of DS1821 temperature sensor.
' According to Dallas Application Note 105, there is an undocumented command for reading
' remain value in DS1821 counter, which is used in standard application for rounding the
' readout (1 Celsius degree resolution). Using this technique it is possible to achive
' 0.5 Celsius degree resolution and an real (not integer) readout!
' Test bed for this program was 89S8252 with minimal hardware, 2x16 LCD and DS1821 connected
' in the following way:
'
' |
' | ---------
' P1.1 +-----o----------------| 270E |-----------o +5V
' | | ---------
' | |
' | | ---------
' P1.0 +-----|---------o------| 4K7 |-----------o +5V
'  | | | ---------
' | | |
' AT89S8252 | o o
' -------------- VDD DQ
'
' Third pin of DS1821 (GND pin) should be connected directly to GND.
'
' =========================================================================================

'-----------------------[Subroutine declarations]---------------------------------

Declare Sub Write_ds1821(addr As Byte , N As Byte)
Declare Sub Mode_toggle_ds1821
Declare Sub Write_stat_ds1821(n As Byte)

'------------------------[variable declarations]---------------------------------

Dim N As Byte
Dim Addr As Byte
Dim Temp_w As Word
Dim Count_remain As Word
Dim Count_per_degree As Word
Dim T As Single
Dim T1 As Single
Dim Sign As String * 1
Dim Tc$ As String * 8

Dq Alias P1.0
Vdd Alias P1.1

'-------------------------[Beginning of Code]------------------------------------

Config 1wire = Dq ' define 1WIRE pin

Cursor Off
Cls
Lcd " DS1821 in "
Lowerline
Lcd " high resolution"
Wait 2
Cls
Lcd " presented by"
Lowerline
Lcd "djdusko@eunet.yu"
Wait 3
For N = 1 To 16
 Shiftlcd Right
 Waitms 150
Next N
Cls

'-----[initialize DS1821]--------------

Mode_toggle_ds1821 ' put device into 1wire mode
Write_stat_ds1821 &H01 ' write in status register:
 ' oneshot measure (IMPORTANT!)
  ' active output low,
 ' power up in 1wire mode

'----------[main loop]------------------

Do
 1wreset ' reset 1WIRE bus
 1wwrite &HEE  ' start conversion (one shot)
!L_wait: ' now...
 1wreset ' reset 1WIRE bus,
 1wwrite &HAC ' read status register,
 N = 1wread()  ' and check,
 mov a,{n} ' does conversion is finished...
 rlc a ' if not,
 jnc L_wait ' loop for a while
 1wreset ' reset 1WIRE bus
 1wwrite &HAA ' and read
 N = 1wread() ' measured value
 Sign = "" ' prepare sign variable

 If N.7 = 1 Then ' if temperature is < 0
 N = 256 - N ' convert it from 2nd complement
 Sign = "-" ' and mark sign
 End If ' (so far it was standard procedure).
 1wreset ' reset 1WIRE bus
 1wwrite &HA0 ' now read remaind part of DS1821 counter
 Count_remain = 1wread(2) ' (it is 9 bit long!)
 1wreset ' reset 1WIRE bus
 1wwrite &H41 ' send LOAD COUNTER command which prepares
 1wreset ' (reset 1WIRE bus)
 1wwrite &HA0  ' for reading the internal parameter
 Count_per_degree = 1wread(2) ' needed for further calculations (9 bits)
 Temp_w = Count_per_degree - Count_remain ' (see details in DALLAS AN105)
 T1 = Count_per_degree 'For T >= 0:
 T = Temp_w / T1 ' Count_per_degree - Count_remain
 T1 = N 'T = N - 1/2LSB + -------------------------------
 If Sign = "" Then ' Count_per_degree
 T1 = T1 - 0.5 '
 T = T1 + T 'For T < 0:
 Else ' Count_per_degree - Count_remain
 T1 = T1 + 0.5 'T = N + 1/2LSB - -------------------------------
 T = T1 - T ' Count_per_degree
 End If  '
 Tc$ = Fusing(t , ##.##) ' format the readout and
 Locate 1 , 4 : Lcd "T=" ; Sign ; Tc$ ; "[C] " ' display measured temperature
Loop ' loop forever

'-------------------------------[DS1821 subroutines]-------------------------------

Sub Write_ds1821(addr As Byte , N As Byte)
 1wreset ' reset 1WIRE bus
 1wwrite Addr ' write command
 1wwrite N ' and then data
End Sub

Sub Mode_toggle_ds1821
$asm
 setb Dq ' rise DQ line
 nop ' (settling time required by DS1821)
 clr Vdd ' now drop VDD line and
 mov a,#15 ' clock DQ line 16 times ...
L_clk: ' (this is the way how to put device
 clr dq ' into 1WIRE mode, if it was previously
 nop ' programmed in thermostat mode)
 setb dq
 djnz a,l_clk
 nop
 setb Vdd ' now rise VDD line (back to normal operation)
$end Asm
End Sub

Sub Write_stat_ds1821(n As Byte)
 1wreset ' reset 1WIRE bus
 1wwrite &H0C ' address status register (write command)
 1wwrite N  ' and write data
End Sub

'---------------------------------[End of Code]----------------------------------