TXT and I2C bus speed

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Re: TXT and I2C bus speed

Beitragvon vleeuwen » 22 Jul 2019, 14:30

Hi Rei,
I also did approach fischertechnik about this issue.
However I am very surprised that this is still an issue. I was out of the practical I2C work because of more important things in live for almost 3 years.
And the discussion about I2C issues like: "a signal output as power supply " give me the idea that the TXT I2C bus was already operating very well.
What me wonder the most is that the FT-community I2C-boys did not notice these kind of elementary problems.

What I also notice is the importance of the right total of Rp's in relation with the total of capacity of the I2C connection lines+ devices.
(See also: viewtopic.php?f=21&t=5376 )
After reading the I2C articles in the FT-pedia's about I2C, I don't understand why these basic issues where not mention.

The NXP specification and user manual is very clear and good readable about this all.
A good reason to repeat the link: https://www.nxp.com/docs/en/user-guide/UM10204.pdf

I was lucky that the 100kHz device PCF8574(A) is able to handle the 400kHz bus speed and that I have I nice logic analyse (LabNation SmartScoop).
But I also can imagine that a normal end-user who rely on the RoboPro I2C 100Khz elements, will not understand why a real 100kHz device is not working properly.

Cordialement
vleeuwen
 
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Re: TXT and I2C bus speed

Beitragvon fotoopa » 22 Jul 2019, 15:15

vleeuwen hat geschrieben:What I also notice is the importance of the right total of Rp's in relation with the total of capacity of the I2C connection lines+ devices.

Which Rp value do you use on the lines now?
fotoopa
 
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Re: TXT and I2C bus speed

Beitragvon vleeuwen » 22 Jul 2019, 15:21

+/- 2k2 ohm.
The total value is not to calculate because the Rp and Rs of the TXT is not specified.
Normally all the TXT in- and output are protected with small serial resistors.
But with only the 10 kOhm from the level shifter it is working too but the shape is in that case not so beautiful.
Zuletzt geändert von vleeuwen am 22 Jul 2019, 17:56, insgesamt 1-mal geändert.
vleeuwen
 
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Re: TXT and I2C bus speed

Beitragvon fotoopa » 22 Jul 2019, 15:38

vleeuwen hat geschrieben:+/- 2k2 ohm.
But with only the 10 kOhm from the level shifter it is working too but the form is in that case not so beautiful.
Thanks!
That's why I placed 1K5 and I don't have any problems with this value.
fotoopa
 
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