2024-02-04 09:10 PM
When I configured development board's I2C I am receiving a short high pulse at 8th clock of SCL.I am attaching the waveform on scope following this post.
Thanking in advance.
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2024-02-07 07:19 PM
Sure, changing to a different slave device might look different.
As TDK has mentioned: you are concerned about a pulse which does not matter (it should not have any effect).
As mentioned:
I have checked again your scope picture: I guess, you are talking about the small spikes on SDA (during the transaction), after the 8th bit, right?
But pretty obvious for me (what I see) and not any issue:
The SDA "must" generate such pulses - on the 9th bit (due to Open Drain logic and "speed" of the slave). Changing to a different slave is a different timing: the other guy is now faster on driving SDA as ACK towards the master and the pulse disappears.
As long as you see "pulses" during SCK is low - all is fine. And such pulses are obvious to get on the 9th bit.
Your "pulses" (on scope picture) should not have any effect (and they are possible and based on the nature how I2C works, dependent on the slave device you use...). All fine!
2024-02-05 05:58 AM - edited 2024-02-05 05:58 AM
There is nothing wrong with that signal. The pulse is due to a switch on which chip that is driving that signal for the ACK bit.
2024-02-05 11:04 PM
Are we talking about bit 9?
Bit 9 is an ACK/NACK: if all is OK, bit 9 is low. If something goes wrong, e.g. wrong I2C slave address (and not any slave is responding) bit 9 is high.
When you say "short high pulse" - remember this:
So, when on the 9th bit the direction changes (the slave wants to set it ACK, going low) - there can be a small pulse seeing at high short before.
You have to bear in mind:
Just look for SDA line when SCK is high (ignore transitions on SDA during SCK low). This can be caused by "changing the direction" and the pull-ups there (causing a high pulse which is not "valid" for master and should be ignored).
2024-02-06 10:33 PM
Dear TDK,
I have paired my I2C pins with another peripheral (i.e TLC59108f) and didn't observe any pulse as i observed in PCF8575.Will it be related to which I2C peripheral i am using.
Thanking you in advance.
2024-02-06 10:37 PM - edited 2024-02-06 10:38 PM
Dear tjaekel,
Thanks for replying.But didn't notice any kind of false pulse when i changed the I2C Peripheral.
2024-02-07 04:45 AM
The pulse isn't a problem. Yes, it may look different with different chips. It doesn't matter, it is not an issue.
2024-02-07 07:19 PM
Sure, changing to a different slave device might look different.
As TDK has mentioned: you are concerned about a pulse which does not matter (it should not have any effect).
As mentioned:
I have checked again your scope picture: I guess, you are talking about the small spikes on SDA (during the transaction), after the 8th bit, right?
But pretty obvious for me (what I see) and not any issue:
The SDA "must" generate such pulses - on the 9th bit (due to Open Drain logic and "speed" of the slave). Changing to a different slave is a different timing: the other guy is now faster on driving SDA as ACK towards the master and the pulse disappears.
As long as you see "pulses" during SCK is low - all is fine. And such pulses are obvious to get on the 9th bit.
Your "pulses" (on scope picture) should not have any effect (and they are possible and based on the nature how I2C works, dependent on the slave device you use...). All fine!