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Dallas/Maxim One Wire Library

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Here is a basic library for 1-wire communication. It works with CPU frequency of 1 MHz or higher. Carefully crafted assembly code is used to allow operation over a wide CPU clock frequency range.  

Thanks to pointers from Rickta59 here's code tuned to work in msp430-gcc. I've used it in my project to read temperature from DS sensor and it works correctly. dow.zip

Hi oPossum (Kevin?),   Combining read/write bit "slot" functions is incredibly insightful. Bravo! After looking at the separate read and write routines on an old DS18B20 + PIC 10F200 project, comb

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Pardon my ignorance, but what is "Dallas/Maxim One Wire"? Is it an asynchronous single-line protocol?


Yes. It's a two wire bus that has a time based protocol. Maxim/Dallas is the only manufacturer in the world.


Here's an excellent summary of it.


Most people use their temperature sensors in their HVAC projects.


But, it's also used in a serious manner. I have a client who has based their entire business on these temperature sensors. They are one of the largest users of one wire technology in the world.

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So I'm having a bit of a problem trying to figure out this code, and I'm wondering if anyone could help me out a bit.


Basically, I'm trying to use G2231 to read a DS18B20. I'm using pin 1.6 and 1 MHz factory calibrated clock.

The thing is, when I send down the initial check owex(0,0), I get correct behaviour (tested on 2 different sensors). 0xFFFF if the sensor is plugged in and 0 if it's not.


Then, I try to send down the Skip Rom command (0xCC) in order to verify the communication. It fails, for it always returns a 0. Curious enough, though, if I send down the ReadRom command (0x33), I do get the echo back (0x33). I'm using the sensor in the pull-up resistor configuration.


I get the feeling I'm missing something basic here. It says in the OP that if I don't get an echo when using 0xCC command, there's a problem on my bus, but I dont actually get what that would mean. I don't have access to an oscilloscope and the voltages check out fine. I'd be grateful for any help.


Here's my main code:

void main(void)

volatile int p;
volatile int test;

WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer



	one_wire_setup(&P1DIR, &P1IN, BIT6, 1);


	p = owex(0,0);

	if(p == 0xFFFF){
		LCD_writeString("D found.");
		test = owex(0xCC, 8);
		LCD_writeString("D not found.");



So basically, if there's a sensor plugged in, I get this on the lcd:

Device found.



If there isn't, I get:

Device not found

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Thanks for the help. Sorry I didn't answer sooner but something unexpected came up.


Yeah, the jumper on 1.6 was removed, I forgot to mention that. Anyway, I'll try running your sample code tomorrow and try to see what comes up.


Thank you very much for your help so far :)



Hah! Found the problem.


I had a "lightbulb" moment and checked to see if I didn't accidentally mistake my DS18B20 for a transistor or something else in TO-92 casing. Funny enough, it seems that my DS18B20 isn't DS18B20 at all, but DS18B20P, which is a Parasite-mode only chip. :lol:

It'll be a while before I can get my hands on a normal one. Will report back then.

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I'm working on implementing this for the IV-18 Clock booster and I'm not sure if I've got things running correctly or if I'm misinterpreting the output


Before the print_temp function executes, the values for TF and TC are around 3304 and 6459.

This is what I'm seeing in the console:


One Wire Test
FF 33 28 53 92 BF 03 00 00 B2 
206.5000 403.6875 


I'm seeing numbers increase when I touch the sensor and back down when I take my finger off and the serial is always consistent.


Any suggestions?

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