OneWire Implementation on Digital Pattern Editor

[gelo88]

Hi!

I am doing a custom onewire implementation where the bitstream logic 1 and 0 is expressed by changing the pulse width within a fixed bit period as shown below (kindly disregard trise and tfall for now)

If the DUT reads "vhigh" level at time = tread (3us) then it reads a "1" (the red waveform), otherwise if it reads "vlow" then "0" (blue waveform).

Using the Digital Pattern Editor, I was able to create a timing waveform for both the logic "1" and "0" and those show up fine when probed with an oscilloscope.

My questions are:

1. How do I simplify sending long bitstreams using the Digital Pattern Editor? For example, if I have to send one byte of data = 0xA3, I have to define each bit on the *.digipat file with the timeset for either logic 1 or 0.
   It looks like below:
   

   But what if I want to sweep the byte value from 0x00 to 0xFF?
   Do I have to create a pattern file that will explicitly define each bit's time set? 

2. What I would like to do is:
   
   
   1. Define a variable, say, "byte_to_send" and assign a value to it.
   2. Create an expression or function within the Digital Pattern Editor that will assign the correct time set for each bit depending on its value.
   3. Assign a new value for byte_to_send and loop 2.1 to 2.2.
3. Or perhaps there's a better way to implement the intended steps above?

Thanks!

[santo_13]

Do you happen to be familiar with Source and Capture waveforms of 657x?

If you're not, you need to take up training sessions from NI.

https://learn.ni.com/learning-paths/device-testing-with-digital-pattern-instruments

The way I would approach this is,

1. Create a digital pattern that uses source waveforms to support writing N-bytes to the device
2. In the test program, write an array of 0x00 to 0xFF to the source waveform and burst the pattern
3. Now, I can reuse the same pattern to write just any data (write to source waveform, burst the pattern)

[gelo88]

Hi!

Thanks for the suggestion.

I have no issues generating the sweep pattern of any byte length.

But I do have trouble assigning the time set for each bit of the pattern I send, because the pulse width for logic "0" is different for logic "1".

Step 3 on your suggestion seem to indicate usage of a single time set (i.e. fixed pulse width). Or maybe I'm missing something?

Thanks!

[santo_13]

Yeah, I am suggesting to create a few vectors that can generically represent a bit in OneWire data and just loop over them to a byte and then N-byte.

If you boil down your timing rules of a bit, you can make the common portions constant and only the different portions as source waveform.

[gelo88]

Hi! Thanks for the suggestion.

Ultimately, I figured that Digital Pattern Editor logic states is level based, not time (pulse width) based as is the case for OneWire.

What worked is to create two timings -- one for logic '1' and another for logic '0'. Both logic states have the same bit period, but differing duty cycle %.

To send each byte, I use a call function to call whatever byte sequence I need. Each possible byte (all 2^8 combinations) is hard-coded with the two timings. 

Kind regards.