P82B96: p82b96

Hi Ali,

For pull up resistors, we have an app note to discuss how you can calculate this. Link here (click me)

We can make the assumption that a cat5 cable has about 50pF of cap per meter. This brings the cap value to 250pF. 

Assuming you communicate at 100kHz or slower (standard mode for I2C). The max pull up resistor you need would be 4.7k (used equation 7 in the app note using 1000ns and 250pF). I would then suggest putting around ~9k pull up resistors on both sides (9k pull ups in parallel are about 4.5k equivalent which is lower than the max 4.7k we calculated). You can adjust these values further once you have things set up and analyze the waveforms on an oscope but I would probably start there.

Ali Khan said:

What should i consider about the delay in programming because it's seems like this delay might be a problem at some stage?

You may need to slow down your I2C frequency if the delay does become a problem but 5 meters likely isn't going to be a huge time of flight issue. I assume since you are monitoring temperature, you don't need to pull data from the temperature sensor very often so using slower frequency shouldn't be a problem unless I am misunderstanding something. 

Ali Khan said:

The voltage that is available on board is 3.3V. What should be +V Cable?

Higher is better for a noise margin perspective on the cable side. 3.3V should still work, if you have a 5V line, I would consider this otherwise 3.3V is fine.

Ali Khan said:

What i should consider while choosing 5 meter cable?

Lower capacitance per meter and lower inductance per meter. You don't need any twisted pairs because this device doesn't use differential signaling. 

One last thing I need to point out. P82B96 uses an offset voltage, VoLSx/Sy of around 800mV. This means anything connected to this device would need to be able to accept this voltage as a logic low. It also has a ViL of 0.65V so devices need to be able to drive below 0.65V to send a low through the device.

-Bobby

Hi

Thanks for your response.
I am not able to download this tool.
Can you help me with it plz?
https://www.ti.com/tool/I2C-DESIGNER

Also,
I have to connect two slave devices with same I2C port.
1:LCD

2: Sensor. It has 4.7K pull up resistor.

It will be almost 3k on each line due to parallel configuration.
If both above resistance values isn't in my control then what i should consider for it?
Also, do you think 3k is enough for standard speed communication as you mentioned max will be 4.7k based on some assumptions.

Thanks

Ali Khan said:

Thanks for your response.
I am not able to download this tool.
Can you help me with it plz?
https://www.ti.com/tool/I2C-DESIGNER

The tool isn't meant to be downloaded, you should be able to use it using your web based browser. I think if you scroll down, you can click the run on cloud button.

Ali Khan said:

2: Sensor. It has 4.7K pull up resistor.

It will be almost 3k on each line due to parallel configuration.
If both above resistance values isn't in my control then what i should consider for it?
Also, do you think 3k is enough for standard speed communication as you mentioned max will be 4.7k based on some assumptions.

P82B96 needs to be used as a pair. You may damage anything that is connected to the cable if you connect it directly to the cable. 

I2C controller |P82B96| ----cable------- |P82B96| sensor

Using 3k is fine since it means ur below the 4.7k required. You just can't be above 4.7k

Hi bobby

Yes, i am not able to use it in clound. When i click on this link, it gives me 404 error.
Check attached screenshot plz.

Hi Ali,

What web browser are you using?

I haven't seen this type of issue pop up before so I'm not quite sure what the error is.

https://www.ti.com/product/TCA9546A?dcmp=dsproject&hqs=pf 

Are you able to click on this link then scroll down to the design/tools section and then click on the I2C designer on there? 

-Bobby

i am using Chrome.
Yes, i am able to click on it and it open a new page. This page is probably in Danish because translator pop up.
But when this link open, it's says 404 Forbidden.

Ali,

I'm not sure what the problem is. I was able to run it from my end and also verified my co-workers are able to access it as well. This may be related to potential firewalls or blocked connections/ports/proxys. I likely won't be able to help debug the I2C designer 404 issue you're seeing unfortunately. 

Are you still unclear about the P82B96 application use?

-Bobby