1-Wire Bus decoding issue ?

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ve7ihl
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1-Wire Bus decoding issue ?

Post by ve7ihl »

I have board using an Atmel 2651 MCU using a port pin that is driving a 1 wire bus to 3 DS2433 eeprom devices. The bus has a 4k7 pull-up resistor to VCC (+5v). I am using a 2205A Pico scope. It is working as expected. When using the Picoscope6 software (Windows) it appears as if the software is decoding the 1-wire-bus byte values in the wrong bit order. For example if a 0xAA value is sent on the bus, the software displays this as 0x55. The LSB/MSB bit are being displayed in the wrong order.
Has anybody seen this?
Do I have something setup wrong?

bennog
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Re: 1-Wire Bus decoding issue ?

Post by bennog »

the signal is probably inverted.

Then you get this kind of mismatch.

Benno

ve7ihl
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Re: 1-Wire Bus decoding issue ?

Post by ve7ihl »

Looking at the actual waveform (with a different bench scope), the waveform looks correct (not inverted). If I try the "inverted" selection on the 1-Wire-bus decoder settings panel, it then dopes not decode anything. it just seems as if the picoscope software is decoding the waveform backwards (MSB to LSB?)

Martyn
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Re: 1-Wire Bus decoding issue ?

Post by Martyn »

Please post a psdata file showing this.
Martyn
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ve7ihl
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Re: 1-Wire Bus decoding issue ?

Post by ve7ihl »

I have provide a .psdata file showing the 1-wire bus decoding. Also did a JPG of the scope screen capture. You can see that the 1st "command code" being decoded is 0xAA, where it should be 0x55 (Match ROM command). I am not sure what is wrong with my setup?
Attachments
Capture.JPG
20210511-0001.psdata
(15.17 KiB) Downloaded 14 times

Martyn
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Re: 1-Wire Bus decoding issue ?

Post by Martyn »

In the 1-wire settings change the threshold from 4V to 2V and you will find it decodes correctly. Some of the pulses in your signal are a bit low.
Attachments
Corrected-1Wire.png
Martyn
Technical Support Manager

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