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Calculating the Correct Pull-up Resistor Value in I2C Bus Applications

What do you see on the bus? Is there any activity? So if it is shorted to GND it will wait forever if there is no timeout in software. I'd look very carefully at the I2C transactions. Some chips can be very picky about stop conditions before a new start condition. There are small lies, big lies and then there is what is on the screen of your oscilloscope. I think you neglected to shift the 7bit I2C address to the left by one bit.

Thanks, exactly that was the error. I have done the same thing. More than once. Factory - the worlds smallest factory. Quote from: rx8pilot on March 04,pm. This is why I love this group. Its hard to make a mistake that someone else has not yet learned the hard way. And yep, I ran into this at the weekend as well with some i2c modules I had bought.

My analog discovery also decoded it the same way as the library named it, so I'm more inclined to say that's the correct way of referring to it. I poured through the i2c specifications, and they really don't deal with the numbing-address convention strongly enough to say that this guy was wrong in his little 3rd party module, but wow, "that's a trap for young players".It's possibile to prevent this hang-over?

It's possible to define a custom function to inspect the bus for 'working' slaves before starting the real communication? You can use the low level function fSendStart to check if a Slave ACKed the start condition and then use high level functions only if the slave was present. Following are the steps. If no ACK, send a Stop and release the bus 2. Would you happen to have a CY and the little I2C slave board with you?

I have a project for this hardware combination. I have up to six slaves on a board and I would like to know which ones are present. I implemented the routine and code suggested above but every thing hangs up after the the master recieves an ACK from 4th slave and. It hangs in the. I have a similar problem and I've been looking through the include files. On the other hand: A timeout would break the standards for I2C.

A timeout was never defined in the protocol. When a running connection dies and your code hangs in the I2C communication, you can reboot your machine using WDT.

How to recover from potential I2C bus lockup?

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Please type your message and try again. I have the same question Show 1 Likes 1. This content has been marked as final. Show 15 replies. Any thoughts on this anyone? Think it would clarify what exactly doesn't work as you expect.

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If not, I'll port to and post it. No, no avail. Any Ideas or help? I have a similiar problem, using I2Cm module.

i2c bus hang

I have a Tech Case being looked at by Cypress. Regards, Dana. Have you received any information back from cypress on solving this problem? Johann, refer to the answer SAMP. CY gave: Timeout is not implemented. Go to original post. Remove from profile Feature on your profile.It is recommended to download any files or other content you may need that are hosted on processors. The site is now set to read only.

Blocked I2C Bus

Some sections may be applicable only to certain devices in which case it will be noted. The reader is encouraged to use data manuals and user guides as the primary source of information.

This article is intended to supplement. The silicon errata for a specific device is also a good place to look for device-specific issues. A very common mistake made by users of the I2C module is to incorrectly configure the clocks. The following diagram is an excerpt from page 14 of sprud c I2C Reference Guide :. Pay close attention to the pieces circled in red. The input clock to the I2C must be between 6.

This number could potentially change by device or process node, so please check the user guide for your specific device. For example, the specifies a range of MHz. In general though, failure to properly configure the prescaler can result in "flaky" behavior from the I2C module. Also notice how the frequency is calculated. Notice the value 'd' inside the calculation and make sure you correlate that value with the table below. Furthermore note that due to the nature of I2C and the requirement to observe potential clock stretching, the observed frequency will actually be a little slower since the I2C peripheral needs to for the clock to rise in case the slave wants to hold it low.

So the slower the rise time the more deviation you'll see from this calculated frequency. A common mistake is to neglect checking for a NACK. When everything is working properly there is no problem. However, checking for a NACK and handling it can save you lots of time. For example, if you have a board with a hardware problem then the NACK detection can quickly help you identify those issues.

Would hang in case we get NACKed! In order to do so you would normally first do a write of the address from which you want to read, followed by a repeated start and then a read of that address. A repeated start can be accomplished by writing to the start bit STT. The only "trick" is to set the bit at the correct time. The bit of interest in this case is the ARDY bit.There are many reasons for a micro controller to go through a reset condition. Watchdog triggering, user events and intentional reconfiguration are only some examples.

For systems which employ an I2C bus such reset of a micro controller may have rather unexpected side effects if other components continue to operate during the reset phase. I2C slaves work as a state machine. After they have been addressed they keep receiving bytes until they see another start condition or a stop condition send by the I2C bus master.

But what if the I2C master goes through a reset right in the middle of transmitting or receiving a byte from the I2C bus slave? One rather clumsy but easy to implement solution is to toggle the clock line multiple 16 times before doing any I2C operation after power-up of the micro controller i.

This sequence can be followed by a stop condition. In many cases this will advance the state machine of any blocked slave to a point where it accepts the next start condition again. A safer but more complex solution is to power cycle all I2C devices after a reset condition. The key point to keep in mind is that an I2C slave is not stateless and therefore may not function properly out of the box after reset or — equally common — a spike caused by EMC influence interpreted as clock signal.

Did you ever see a blocked I2C bus? No communication after reset? In other words, the bus is stuck, your I2C bus is blocked.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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i2c bus hang

Sign in to your account. This situation is known and described e. On an oscilloscope both lines remained high. After this code:.

I get the line high again but cannot get I2C working again without pulling the reset line low. Hence I would appreciate any hint in getting this resolved inline. Maybe the recovery could also be added to the library? Want to back this issue? Post a bounty on it!

We accept bounties via Bountysource. I will try it later today and will let you know here. I see it is written for Atmel but apart from the line below I think everything runs on ESP as well.

To me it seems something in the OS. If you want me to try something else, please let me know. I could even tweek libraries but would need some guidance. At the moment I have no idea why would Wire library stop operating after this restart. Once this is determined and fixed, we can proceed to add this recovery code to the library itself. If you have capacity to investigate this, Wire library source is here and software I2C implementation is here.

Will come back on this later at the end of the week.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts.

It only takes a minute to sign up. I am very new to electronics and have entered in the territory of I2C bus. Want to understand the behaviour of compliant devices as per I2C protocol specification. One condition as per the link below is when a master controller is reset in midst of a transaction. That is to say the slave engaged does not knows what to do now. I do not understand how does this calls for bus hang? The master which was restarted could always start a new transaction and the slaves should be able to read it.

If there is only one slave on the bus, the worst-case scenario would be when the the master is reset just after the slave has just been issued a "read" request, was in the process of acknowledging it, and is all set to send a "0" in response. In that scenario, the first clock would advance past the ack, and the next eight would advance past the data bits, and the device would drive SDA continuously until it receives the ninth clock.

After the clock goes high then low the ninth time, however, the device would float the bus if it hadn't done so before to look for an ack from the master. If there are multiple slave devices, a bus could become permanently locked up if two devices both think they've received commands to read out a string of zero bytes, but possibly because the master was reset at a time that resulted in a "runt" pulse on SCL that was long enough to be seen by one slave but not the other the two slaves release the bus at different times when looking for acks from the master.

Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. What are the various ways in which an I2C bus may hang Ask Question.

Asked 2 years, 2 months ago. Active 2 years, 2 months ago. Viewed 1k times. Is there any other way in addition to the what is explained above to cause a bus hang?

Can such a problem be caused by software driver? As simple as this. Jan 15 '18 at I think understand that part - however I don't get it what would cause a line to be permanently pulled down - and then what makes it to release it. Active Oldest Votes. Can you please clarify on "In that scenario, the first clock would advance past the ack, and the next eight.

i2c bus hang

What is "first clock" in the context and what is "next eight"? Also if you could answer how this could be caused by a software driver? Inopportune reset? Two slaves releasing bus at different times causes hang?

How two slaves can start responding simultaneously, as the address may have matched only one? Depending upon how sensitive the slaves are to different pulse widths, it may be very unlikely that such an issue might occur. On the other hand, if it does occur, recovery may be impossible. Sign up or log in Sign up using Google.Pages: [1]. New to both the hardware and software of development.

Currently trying to use Arduino to make farm chores easier. And so on I2C hang. I have 2 Uno R3 boards talking back and forth to each other via I2C simple messages. All is well. No problems. When I pull power on either board to simulate a fault in the wire, dead battery, failed board, etc the other board hangs at the wire.

This is the exact spot it hangs. I can;t even get a return code: just freezes. If I power up the "broken" board and chatter returns to normal like nothing happened. I am a beginner and do not have an IT background. Any suggestion in the right direction is appreciated. Re: I2C hang. Currently built mega http server, Now converting it to ESP I am going to look into the PCAA.

Thank you for explaining to me what the darn thing is and what the issues are I am not sure what to comment or modify in your files but I will try my best.

I am new to programming and Arduino so still kinda flying blind I too experienced the problem of my code hanging up when one of my slave Arduinos lost power but I was able to create a workaround to this problem while still using the default Wire library. By using an Arduino relay shield I was able to bypass the slave that lost power and detect this loss with a!