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Peter63
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Joined: 28/07/2017
Location: Sweden
Posts: 196

Posted: 05:35am 30 May 2026

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Jepp

Bryan1

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Joined: 22/02/2006
Location: Australia
Posts: 2099

Posted: 05:47am 30 May 2026

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Well I decided to setup my 2040 Zero with that ili9488 now it's free and gave this DS1820 code a go, now I was having no luck so went back to the start of this thread and saw Tempr(GP9,500) was the fix to get the DS1820 working.

Now when I run the code.

50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 680°C
50
Temp = 154°C
50
Temp = 154°C
50
Temp = 154°C
50
> ? tempr (Gp9, 500)
19.25
>

Nothing changed in the code just copied it and pasted into MMEdit. Anyway the good thing the DS1820 looks to be working

phil99

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Posts: 3291

Posted: 06:13am 31 May 2026

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Ok, so if you don't know which DS18x20 you have these two functions should work with any, including slow ones.
In the first one you can optionally set the Conversion Time in mS.
Usage:-
Print DS18x20ct(mm.info(pinno GPxx)) ' the default Conversion Time is 750mS
or
Print DS18x20ct(mm.info(pinno GPxx, mS_delay) '1000mS should cover most.

The second doesn't need it as it checks if the conversion is finished before reading. If not finished it returns to the main loop.
After reading it starts a new conversion, whish happens in the background as it returns to the main loop.
Usage:-
Print DS18x20(mm.info(pinno GPxx))

Function DS18x20ct(PinNbr As INTEGER, Delay As INTEGER) As FLOAT
' derived from DS18x20 test code by TassyJim
Local INTEGER T1,T2,T3,CpC,F
OneWire WRITE PinNbr,1,1,&h33 'read "family" ROM code
OneWire READ PinNbr,0,1,F ':Print F, "16=DS1820/DS18S20, 32=DS18S22, 40=DS18B20",
OneWire RESET PinNbr ' reset before command
OneWire WRITE PinNbr, 8, 2, &hCC, &h44 ' start conversion, adjust for slow units
If Delay < 10 then Delay = 750 ' maximum normal conversion time
Pause Delay
OneWire RESET PinNbr ' reset before command
OneWire WRITE PinNbr, 1, 2, &hCC, &hBE ' command read data
OneWire READ PinNbr, 0, 8, T1,T2,T3,T3,T3,T3,T3,CpC 'get the data
'process the data
If F=16 Then DS18x20ct = Str2bin(int16,Chr$(T1)+Chr$(T2))\2 -0.25 + (CpC-T3)/CpC
If F=40 or F=34 Then DS18x20ct = Str2bin(int16,Chr$(T1)+Chr$(T2))/16
End Function

PinNbr = MM.Info(pinno GP7)
Dim DStemp = DS18x20(PinNbr) 'purge old data and start new conversion
Dim integer n

Do 'Main Loop
t = timer
Print n;
DStemp = DS18x20(PinNbr) 'get Temp, if ready
If DStemp <> 1000 Then
Print
Print "Temp =";DStemp;"`C"
n = 0
EndIf
Do : Loop until Timer > 49.9
inc n,50
Loop

Function DS18x20(PinNbr As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
Local INTEGER done, T1, T2, T3, CpC, F
DS18x20 = 1000 ' standard error code
OneWire READ PinNbr, 4, 1, done ' is conversion finished?
If done = 0 Then Exit Function ' if not return to program
'Get the data
OneWire WRITE PinNbr,1,1,&h33 'read "family" ROM code
OneWire READ PinNbr,0,1,F ':Print F; " 16=DS1820/DS18S20, 32=DS18S22, 40=DS18B20",
OneWire RESET PinNbr ' reset before command
OneWire WRITE PinNbr, 1, 2, &hCC, &hBE ' command read data
OneWire READ PinNbr, 0, 8, T1,T2,T3,T3,T3,T3,T3,CpC ' get the data
' process the data
If F=16 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))\2 -0.25 + (CpC-T3)/CpC
If F=40 or F=34 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))/16
DS18x20 = Cint(Value * 10) / 10 'round to 1/10ths

'Start conversion, ready for next read
OneWire RESET PinNbr ' reset before command
OneWire WRITE PinNbr, 8, 2, &hCC, &h44 ' start conversion
End Function
End

Bryan1

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Joined: 22/02/2006
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Posts: 2099

Posted: 07:00am 31 May 2026

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Thanks for that Phil

just tried it

Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 85°C
50
Temp = 18.1°C
50
Temp = 18.1°C
50
Temp = 18.1°C
50
Temp = 18.1°C
50
Temp = 18.1°C
50

I did get these sealed can temp sensors about 15-16 years ago so they may be DS1820's that need the delay for it to work.

Anyway it is time to make a new thread with my project for the temp sensor.

Regards Bryan

phil99

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Posts: 3291

Posted: 12:32pm 31 May 2026

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Have been puzzled by your output only showing "50" between reads. Each 50 is 50mS so you should get something like this.

50 100 150 200 250 300 350 400 450 500
Temp = 19.2`C
50 100 150 200 250 300 350 400 450 500
Temp = 19.3`C

Then when I tried a non-genuine DS18B20 I got the same as you. Further investigation showed it says it has completed the temperature conversion in 33mS.
But it hasn't actually finished so the data you get is from a previous read.
That is why you got a string of 85°C readings, then the correct temp.

For these non-genuine units you are better off using the MMBasic TEMPR START GPxx,3 before the TEMPR(GPxx) function. The ",3" gives maximum resolution and ensures TEMPR(GPxx) waits long enough before reading.

The example above shows TEMPR(GPxx) immediately following TEMPR START but it doesn't need to. You can put other code between to make use of the 600mS or so it takes to do a conversion.
Edited 2026-06-01 08:00 by phil99

phil99

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Posted: 10:56pm 31 May 2026

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More experimenting with the nongenuine DS18B20.

It's conversion time is much faster than for the genuine unit.
It does high res 1/16° conversions in less than 34mS.
With the temperature changing rapidly it really does get new values that fast.

It's accuracy, however appears to be a little less, almost 1° high compared to a genuine unit and a pair of AHT10s.

Edit.

> 'Non-genuine DS18B20
> t2=timer:OneWire WRITE 9,1,2,204,68:t=timer:do:OneWire READ 9,4,1,d:loop until d :? timer-t,timer-t2
33.237 35.562
> ' So about 2.3mS to start conversion and 33.3mS to carry it out.
>'genuine DS18B20
> t2=timer:OneWire WRITE 10,1,2,204,68:t=timer:do:OneWire READ 10,4,1,d:loop until d:?timer-t,timer-t2
479.366 481.694
>

Edited 2026-06-01 11:09 by phil99

phil99

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Posts: 3291

Posted: 08:57am 02 Jun 2026

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A number of DS18x20 can run from the same OneWire bus by using the unique ROM code each contains.
The codes can be read by copying and pasting the command lines below into TeraTerm.
Only one device may be on the bus while reading the code. Ignore the output numbers in the example

> clear : dim integer q,w,e,r,t,y,u,i,ROM, PinNo=mm.info(pinno GP6)
> OneWire Reset PinNo : OneWire WRITE PinNo,1,1,&h33 : OneWire READ PinNo,2,8,q,w,e,r,t,y,u,i : ? ,q,w,e,r,t,y,u,i
40 63 68 87 4 225 60 77
> RC$ = chr$(q)+chr$(w)+chr$(e)+chr$(r)+chr$(t)+chr$(y)+chr$(u)+chr$(i) : ROM = str2bin(Uint64,RC$,big) :? ROM
2900111825584602189
>

Its a bit clunky but OneWire doesn't use arrays or strings.

Insert your ROM code numbers and OneWire pin number in the program below. This example is for two but could be modified for more.

' running 2 DS18x20 sensors on the same pin. Get their ROM codes an replace those below
Dim PinNbr = MM.Info(pinno gp6)
Dim integer n, ROMcode(1) = (2909716863767585976, 2900111825584602189)

Dim DStemp0 = DS18x20(PinNbr, ROMcode(0)) 'purge old data and start new conversion
Dim DStemp1 = DS18x20(PinNbr, ROMcode(1)) 'purge old data and start new conversion

Do ' Main Loop
D = DS18x20(PinNbr, ROMcode(n))
If D<>1000 Then Print "Device";n; D;"`C",
If n=1 Then Print
Pause 1000
n = Not n
Loop

Function DS18x20(PinNbr As INTEGER, ROM As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
Local INTEGER done, T1, T2, T3, CpC, Fam, a,b,c,d,e,f,g,h
DS18x20 = 1000' standard error code
OneWire READ PinNbr, 4, 1, done' is conversion finished?
If done = 0 Then Exit Function ' if not return to program

If ROM Then
a=ROM>>56 : b=ROM>>48 And 255 : c=ROM>>40 And 255 : d=ROM>>32 And 255
e=ROM>>24 And 255 : f=ROM>>16 And 255 : g=ROM>>8 And 255 : h=ROM And 255
Fam=a ': Print a,b,c,d,e,f,g,h
OneWire WRITE PinNbr,1,1,&h55 ' reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h ' send ROM Code
OneWire WRITE 9,0,1,&hBE ' read scratchpad command
OneWire READ 9, 0, 8, T1,T2,T3,T4,T5,T6,T7,CpC' get the data
Else
OneWire WRITE PinNbr,1,1,&h33 ' read "family" ROM code
OneWire READ PinNbr,0,1,Fam
EndIf

' process the data 16=DS1820/DS18S20, 32=DS18S22, 40=DS18B20
If Fam = 16 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))\2 -0.25+(CpC-T3)/CpC
If Fam = 40 Or Fam = 34 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))/16
DS18x20 = Cint(Value * 100) / 100 'round to 1/100ths

' Start conversion, ready for next read
If ROM Then
OneWire WRITE PinNbr,1,1,&h55 'reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h 'send ROM Code
OneWire WRITE PinNbr,2,1,&h44 'Master issues Convert Temp. command
Else
OneWire RESET PinNbr' ' reset before command
OneWire WRITE PinNbr, 8, 2, &hCC, &h44' ' start conversion
EndIf
End Function
End

Footnote added 2026-06-02 21:49 by phil99
A sample of the output.

Device 0 24.19`C Device 1 31.69`C
Device 0 23.38`C Device 1 31.56`C
Device 0 22.69`C Device 1 31.44`C
Device 0 22.13`C Device 1 31.25`C
Device 0 21.63`C Device 1 31.13`C
Device 0 21.25`C Device 1 31`C
Device 0 20.88`C Device 1 30.88`C
Device 0 20.63`C Device 1 30.75`C
Device 0 20.38`C Device 1 30.63`C
Device 0 20.19`C Device 1 30.5`C

Footnote added 2026-06-02 22:01 by phil99
Noticed a copy/paste error tat would affect the fractions of degrees for DS18S20 sensors.
Replace this line:-
OneWire READ 9, 0, 8, T1,T2,T3,T4,T5,T6,T7,CpC' get the data
with
OneWire READ 9, 0, 8, T1,T2,T3,T3,T3,T3,T3,CpC' get the data

Most of the T3s are dummys, only the one before CpC gives the fractions.

Footnote added 2026-06-11 12:04 by phil99
Found another copy / paste error, going senile.
So here is the function again with all errors fixed.

Quote Function DS18x20(PinNbr As INTEGER, ROM As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
Local INTEGER done, T1, T2, T3, CpC, Fam, a,b,c,d,e,f,g,h
DS18x20 = 1000' standard error code
OneWire READ PinNbr, 4, 1, done' is conversion finished?
If done = 0 Then Exit Function ' if not return to program

If ROM Then
a=ROM>>56 : b=ROM>>48 And 255 : c=ROM>>40 And 255 : d=ROM>>32 And 255
e=ROM>>24 And 255 : f=ROM>>16 And 255 : g=ROM>>8 And 255 : h=ROM And 255
Fam=a ': Print a,b,c,d,e,f,g,h
OneWire WRITE PinNbr,1,1,&h55 ' reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h ' send ROM Code
Else
OneWire WRITE PinNbr,1,1,&h33 ' read "family" ROM code
OneWire READ PinNbr,0,1,Fam
EndIf
OneWire WRITE PinNbr,0,1,&hBE ' read scratchpad command
OneWire READ PinNbr, 0, 8, T1,T2,T3,T3,T3,T3,T3,CpC' get the data

' process the data 16=DS1820/DS18S20, 32=DS18S22, 40=DS18B20
If Fam = 16 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))\2 -0.25+(CpC-T3)/CpC
If Fam = 40 Or Fam = 34 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))/16
DS18x20 = Cint(Value * 100) / 100 'round to 1/100ths

' Start conversion, ready for next read
If ROM Then
OneWire WRITE PinNbr,1,1,&h55 'reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h 'send ROM Code
OneWire WRITE PinNbr,2,1,&h44 'Master issues Convert Temp. command
Else
' OneWire RESET PinNbr' ' reset before command
OneWire WRITE PinNbr, 1, 2, &hCC, &h44' ' start conversion
EndIf
End Function
End

Footnote added 2026-06-11 13:46 by phil99
I just keep making mistakes. This time lucky?
Added a feature. If there is only one device on the bus and an integer variable with a value of 0 is supplied as the ROM Code it will be filled with the device ROM Code. So you can get the ROM Codes of devices without using 1Wire commands.
Eg.

> ? "Temp.";ds18x20(2,code%);"`C", "ROM Code";code% 'only one on the bus
Temp. 21.5`C ROM Code 2900111825584602189
>
> ? ds18x20(2,2900111825584602189), ds18x20(2,2909716863767585976) 'multiple on the bus
21.5 22.25
>

And the amended function.

Function DS18x20(PinNbr As INTEGER, ROM As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
Local INTEGER done, T1, T2, T3, CpC, Fam, a,b,c,d,e,f,g,h
DS18x20 = 1000' standard error code
OneWire READ PinNbr, 4, 1, done' is conversion finished?
If done = 0 Then Exit Function ' if not return to program

If ROM Then
a=ROM>>56 : b=ROM>>48 And 255 : c=ROM>>40 And 255 : d=ROM>>32 And 255
e=ROM>>24 And 255 : f=ROM>>16 And 255 : g=ROM>>8 And 255 : h=ROM And 255
Fam=a ': Print a,b,c,d,e,f,g,h
OneWire WRITE PinNbr,1,1,&h55 ' reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h 'send ROM Code
OneWire WRITE PinNbr,0,1,&hBE ' read scratchpad command
Else
OneWire WRITE PinNbr,1,1,&h33 ' read "family" and ROM code
OneWire READ PinNbr,0,8,Fam,b,c,d,e,f,g,h
ROM=(Fam<<56)+(b<<48)+(c<<40)+(d<<32)+(e<<24)+(f<<16)+(g<<8)+h
OneWire WRITE PinNbr,1,2,&hCC,&hBE ' read scratchpad command
EndIf
OneWire READ PinNbr, 2, 8, T1,T2,T3,T3,T3,T3,T3,CpC' get the data

' process the data. Fam - 16=DS1820/DS18S20, 32=DS18S22, 40=DS18B20
If Fam = 16 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))\2 -0.25+(CpC-T3)/CpC
If Fam = 40 Or Fam = 34 Then Value = Str2bin(int16,Chr$(T1)+Chr$(T2))/16
DS18x20 = Cint(Value * 100) / 100 'round to 1/100ths

' Start conversion, ready for next read
If ROM Then
OneWire WRITE PinNbr,1,1,&h55 ' reset then match ROM Code command
OneWire WRITE PinNbr,0,8,a,b,c,d,e,f,g,h 'send ROM Code
OneWire WRITE PinNbr,2,1,&h44 ' Master issues Convert Temp. command
Else
OneWire WRITE PinNbr, 1, 2, &hCC, &h44' start conversion
EndIf
End Function
End

matherp
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Posted: 10:05am 02 Jun 2026

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phil99: what firmware version are you using? I'll post an update with flexible onewire data parameters for you to test

phil99

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Posted: 10:56am 02 Jun 2026

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PicoMiteVGA MMBasic RP2350A Edition V6.03.00RC12

Or plain RP2040 would also do.

Thanks very much for considering this.

phil99

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Posted: 05:39am 03 Jun 2026

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The latest PicoMite firmware - V6.03.00RC15 can now use strings and arrays in OneWire commands.
Here is the previous program converted to use both. A more streamlined result and simpler to write.

' Running 2 DS18x20 sensors on the same pin. Get their ROM codes and replace those below.
Dim PinNbr = MM.Info(pinno gp6)
Dim integer n=0, ROMcode(1) = (2909716863767585976, 2900111825584602189)

Dim DStemp0 = DS18x20(PinNbr, ROMcode(0)) 'purge old data and start new conversion
Pause 750
Dim DStemp1 = DS18x20(PinNbr, ROMcode(1)) 'purge old data and start new conversion

Do ' Main Loop
D = DS18x20(PinNbr, ROMcode(n))
If D<>1000 Then Print "Device";n; D;"`C",
If n=1 Then Print
Pause 1000
n = Not n
Loop

Function DS18x20(PinNbr As INTEGER, ROM As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
' This version for MMbasic v6.03.00RC15 with array and string support for OneWire
  Local INTEGER done, T(7), Fam = ROM >> 56 'get family code from ROM code
  Local ROMcode$ = Bin2str$(Uint64,ROM,big) 'convert ROM code to string
  DS18x20 = 1000' standard error code
  OneWire READ PinNbr, 4, 1, done' is conversion finished?
  If Not done Then Exit Function ' if not return to program

  If ROM Then
   OneWire WRITE PinNbr, 1, 1, &h55 ' reset then match ROM Code command
   OneWire WRITE PinNbr, 0, 8, ROMcode$ ' send ROM Code to the DS18x20
   OneWire WRITE PinNbr, 0, 1, &hBE ' read scratchpad command
   Else
   OneWire WRITE PinNbr,1,1,&h33 'If no ROM code given assume only one DS18x20 connected
   OneWire READ PinNbr, 0, 1, Fam ' read "family" ROM code
   OneWire WRITE PinNbr, 1, 2, &hCC, &hBE ' command read data
  EndIf
  OneWire READ PinNbr, 0, 8, T() ': Math V_Print T()' get the data

' process the data. Fam = Family ROM codes - 16=DS1820/DS18S20, 34=DS18S22, 40=DS18B20
  If Fam = 16 Then Value = Str2bin(int16,Chr$(T(0))+Chr$(T(1))\2 -0.25+(T(7)-T(6))/T(7))
  If Fam = 40 Or Fam = 34 Then Value = Str2bin(int16,Chr$(T(0))+Chr$(T(1)))/16
  DS18x20 = Cint(Value * 100) / 100 'round to 1/100ths

' Start conversion, ready for next read
  If ROM Then
   OneWire WRITE PinNbr, 1, 1, &h55 'reset then match ROM Code command
   OneWire WRITE PinNbr, 0, 8, ROMcode$ 'send ROM Code
   OneWire WRITE PinNbr, 2, 1, &h44 'Master issues Convert Temp. command
   Else
   OneWire RESET PinNbr' ' reset before command
  OneWire WRITE PinNbr, 8, 2, &hCC, &h44' ' start conversion
  EndIf
End Function
End

Output.

Device 0 13.06`C Device 1 22.56`C
Device 0 23`C Device 1 22.56`C
Device 0 23.06`C Device 1 22.56`C
Device 0 23.06`C Device 1 22.56`C
Device 0 23.06`C Device 1 22.5`C

Reading the ROM codes is simpler too.

> clear : dim integer ROM, PinNo=mm.info(pinno GP6)
> OneWire WRITE PinNo, 1, 1, &h33 : OneWire READ PinNo, 2, 8, RC$
> ROM = str2bin(Uint64,RC$,big) : ? ROM
2909716863767585976
>

Edited 2026-06-03 23:01 by phil99

phil99

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Posted: 05:05am 04 Jun 2026

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Attempts to get the DS18B20s to work in Parasite Power mode have failed so here is a hardware solution that does work.

The component values are not critical, try whatever you have. I have also tested 1.2kΩ and 10µF powering two DS18B20s.

phil99

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Posted: 01:09pm 05 Jun 2026

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Yet another tweak.
As before many DS18x20s can be on the OneWire bus if the unique ROM code of each is provided.
If no ROM code is provided it assumes there is only one device on the bus and reads the temperature and its unique ROM code.
The ROM code is then available in a integer variable with an initial value of 0 in place of the second parameter, The Family Code can be obtained from that by down shifting 56.

Eg, reading 2 individual devices on pins 9 and 10.

> code%=0 : ? "Temp.";ds18x20(10,code%);"`C",,"ROM Code ="; code%, "Family =";code%>>56
Temp. 19.6875`C ROM Code = 2909716863767585976 Family = 40
>
> code%=0 : ? "Temp.";ds18x20(9,code%);"`C","ROM Code ="; code%, "Family =";code%>>56
Temp. 20.0625`C ROM Code = 2900111825584602189 Family = 40
>

For 2 or more on the same pin:-

> clear : PinNo = mm.info(pinno GP6)
> ? ds18x20(PinNo, 2900111825584602189), :pause 500 :? ds18x20(PinNo, 2909716863767585976)
21.375 21.4375
>

Family ROM codes - 16 = DS1820/DS18S20, 34 = DS18S22, 40 = DS18B20

Function DS18x20(PinNbr As INTEGER, ROM As INTEGER) As FLOAT
' Adapted from DS18x20 test code by TassyJim
' This version for MMbasic v6.03.00RC15 with array and string support for OneWire
Local INTEGER done, T(7), Fam, ROM1
Local ROMcode$ = Bin2str$(Uint64,ROM,big) 'convert ROM code to string
DS18x20 = 1000' standard error code

OneWire READ PinNbr, 4, 1, done' is conversion finished?
If Not done Then Exit Function ' if not return to program

If ROM Then
Fam = ROM >> 56 ' extract "family" from ROM code
OneWire WRITE PinNbr, 1, 1, &h55 ' reset then match ROM Code command
OneWire WRITE PinNbr, 0, 8, ROMcode$ ' send ROM Code to the DS18x20
OneWire WRITE PinNbr,0,1,&hBE ' read scratchpad command
Else
OneWire WRITE PinNbr, 1, 1, &h33 'If no ROM code given assume only one DS18x20 connected
OneWire READ PinNbr, 0, 8, ROMcode$ ' read the ROM code
OneWire WRITE PinNbr, 1, 2, &hCC, &hBE ' read scratchpad command
ROM1 = Str2bin(Uint64,ROMcode$,big) ' Output the ROM code to a variable% if it's value was 0
Fam = ROM1 >> 56 ' extract "family" from ROM code
EndIf
OneWire READ PinNbr, 2, 8, T() ' : Math V_Print T()' get the temperature data

' process the data, Family ROM codes - 16=DS1820/DS18S20, 34=DS18S22, 40=DS18B20
If Fam = 16 Then Value = Str2bin(int16,Chr$(T(0))+Chr$(T(1))\2 -0.25+(T(7)-T(6))/T(7))
If Fam = 40 Or Fam = 34 Then Value = Str2bin(int16,Chr$(T(0))+Chr$(T(1)))/16
If Fam = 0 Then Value = 1001
DS18x20 = Value

' Start conversion, ready for next read
If ROM Then
OneWire WRITE PinNbr, 1, 1, &h55 'reset then match ROM Code command
OneWire WRITE PinNbr, 0, 8, ROMcode$ 'send ROM Code
OneWire WRITE PinNbr, 8, 1, &h44 'Master issues Convert Temp. command
Else
OneWire RESET PinNbr' ' reset before command
OneWire WRITE PinNbr, 8, 2, &hCC, &h44' ' start conversion
EndIf
ROM = ROM1 ' : Print "conversion started"
End Function

The code above has been edited to improve a couple of minor items.

Checking for a genuine DS18B20 vs. non-genuine.

Genuine units retain the Last Temperature (bytes 0 & 1), High Alarm (byte 2), Low Alarm (byte 3) and Resolution (byte 4) of Scratchpad memory in EEPROM.
On power-up they are restored. Non-genuine ones don't appear to have EEPROM so are in a Factory Fresh state when powered up.

This command-line program shows the difference.

> clear : Dim integer S(8) : Pin% = MM.Info(pinno gp6)
> 'Genuine DS18B20
> OneWire WRITE Pin%, 1, 2, &hCC, &hBE : OneWire READ Pin%, 2, 9, S() : Math V_Print S()
144, 1, 85, 5, 127, 165, 165, 102, 180
> 'Last_Temp = Byte0 / 16 + Byte1 * 16, High_Alarm = Byte2, Low_Alarm = Byte3, Resolution = Byte4 >> 5, CRC value - Byte8
> 'the alarm temperatures have a fixed resolution of 1.0`C
>
> 'Non_genuine DS18B20
> OneWire WRITE Pin%, 1, 2, &hCC, &hBE : OneWire READ Pin%, 2, 9, S() : Math V_Print S()
80, 5, 255, 255, 127, 255, 255, 255, 31
> 'Default_Temp = 85`C = Byte0 / 16 + Byte1 * 16, High_Alarm = Byte2, Low_Alarm = Byte3, Resolution = Byte4 >> 5 These only have resolution 3 so this byte must be 127.
> 'the alarm temperatures have fixed a resolution of 1.0`C
>

Setting temperature alarm levels and reading the alarm status.

While the temperature of all units on the bus is within their set limits the status is 1
If the temperature any of the units on the bus goes high or low the status is 0.
They do not read the temp. unless instructed and there is no provision for triggering an interrupt.
So your main loop needs to trigger a bus-wide read and poll the status periodically to see if a 0 is returned.

If that returns 0 you can read each unit to find which one is out of its limits.

If your program is regularly reading all temperatures none of this is necessary as you can compare the temperatures with ones set in the program.
Either hard coded or from VAR SAVE / RESTORE.
MMBAsic makes life easier.

This Function sets the alarm limits and resolution and returns the ROM code.
It will work with just one on the bus, in which case you don't need to supply a ROM code.
If more than one you must supply the ROM code of the one you are setting the limits and resolution on.
The temperature resolution format is the same as the TEMPR START command.
0 = 0.5°C, 1 = 0.25°C, 2 = 0.125°C and 3 = 0.0625°C
The alarm setting resolution is fixed at 1°C

Function AlarmSet(Pin%, TH, TL, Res%, ROM%) As Integer
'Set the high temp alarm (TH), low temp alarm (TL) and resolution (Res%) of DS18S20 and DS18B20.
Local integer TD(7), done
Local ROMcode$, t
TH = Cint(TH) And 255 : TL = Cint(TL) And 255 : Res% = ((Res% And 3) << 5) + 31 'prepare the data

t=Timer 'Start conversion on all units on the bus and wait for the slowest to finish.
OneWire WRITE Pin%, 1, 2, &hCC,&h44
Do
OneWire READ Pin%, 4, 1, done
Loop Until done Or Timer - t > 1100 ' : Print Timer-t;"uS conversion time"

If ROM% Then ' 1 or more devices on 1Wire bus, ROM Code supplied
ROMcode$ = Bin2str$(Uint64,ROM%,big) ' convert ROM code to string
OneWire WRITE Pin%, 1, 1, &h55 ' reset then match ROM Code command
OneWire WRITE Pin%, 0, 8, ROMcode$ ' send ROM Code
OneWire WRITE Pin%, 0, 1, &hBE ' Read data command (to to check for non-genuine DS18B20)
OneWire READ Pin%, 0, 8, TD() ': Print "TD() = "; :Math V_Print TD()' read back the scratchpad data
If TD(7) = 255 Then Res% = 127 ' Non-Genuine DS18B20 use resolution 3 only
OneWire WRITE Pin%, 1, 1, &h55 ' reset then match ROM Code command
OneWire WRITE Pin%, 0, 8, ROMcode$ ' send ROM Code
OneWire WRITE Pin%, 0, 1, &h4E ' Write data command
OneWire WRITE Pin%, 0, 3, TH, TL, Res% ' send 3 bytes
OneWire WRITE Pin%, 0, 1, &h48 'transfer the TH, TL and Res data from the scratchpad to EEPROM
Else ' Only 1 device on the bus and ROM Code not supplied
OneWire WRITE Pin%, 1, 1, &h33 ' reset then read the ROM code command
OneWire READ Pin%, 0, 8, ROMcode$ ' Get the 8 byte ROM code
ROM% = Str2bin(Uint64,ROMcode$,big) ' Output the ROM code to variable ROM% (if ROM% was 0)
OneWire WRITE Pin%, 1, 2, &hCC, &hBE ' Read data command (to to check for non-genuine DS18B20)
OneWire READ Pin%, 2, 8, TD() ': Print "TD() = "; :Math V_Print TD()' read back the scratchpad data then reset
If TD(7) = 255 Then Res% = 127 ' Non-Genuine DS18B20 use resolution 3 only
OneWire WRITE Pin%, 1, 2, &hCC, &h4E ' reset then write data to scratchpad command
OneWire WRITE Pin%, 0, 3, TH, TL, Res% ' send 3 bytes
OneWire WRITE Pin%, 1, 1, &h48 ' reset then transfer the TH, TL and Res from scratchpad to EEPROM
EndIf

AlarmSet = ROM%
End Function

Reading the alarm status.

t = Timer + 2001 'An example of reading the temperature alarm status of all units on the bus.
Do 'Your main loop

If Timer - t > 2000 Then 'Start conversion on all units at 2 Sec intervals
OneWire WRITE Pin%, 1, 2, &hCC,&h44
t = Timer
EndIf

OneWire READ Pin%, 4, 1, done ' and wait for the slowest to finish.
If done then
OneWire WRITE Pin, 1, 11, &hEC : OneWire READ Pin, 4, 1, alarm ': ? a 'Alarm Search then read all alarm flags
If alarm = 0 then
Print "A temperature is out of limits"
'now read each unit individually to find the culprit
EndIf
EndIf
Loop

Edited 2026-06-20 08:18 by phil99

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