Just read the Application Notes already cited, and work from there.

It's really quite simple: you just need to start with 4 basic routines:

Generate a 1-Wire Reset;

Write a '1' bit;

Write a '0' bit;

Read a bit.
(in fact, if you're smart, you'll spot that you don't actually need a separate Write-1 function...)

These routines are simply a matter of setting the port pin high or low, and reading the line state, with appropriate delays in between. That is all they do - nothing complicated.
You can just take the 'C' code shown in the Application Notes as your specification, and implement it in assembler.

Once you have those basic bit-handling functions, you then just need to read the Datasheet to find the necessary command sequences - and implement then using your bit-handling functions.

You might want to create intermediate routines to do things like read/write a byte, read the device ID, etc...