How many devices i2c bus

Note how we have both 5-volt and 3. Just be sure to tie all of the power supply grounds together. The arrangement works equally as well when powering the TCAA with a 3. You always want to power the module using the host controller. Having two sensors or displays with the same fixed I2C address need not be a show-stopper. By using a multiplexer like the TCAA, or an alternate I2C software library, you can implement multiple I2C buses to resolve any address conflicts you encounter. With its additional capability of using multiple voltage I2C buses, the TCAA is my choice for solving bus conflicts.

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The most important issue is the communication protocol. I look forward to your return.. I try with and without external 5V supply better response time with external one.

No display…. Are you are of these kind of limitation? Displays results on two x 32 OLED displays. Uses Adafruit AM Library. DroneBot Workshop TCAA 1 ;. TCAA 2 ;. What are the physical limiting factors? The software limiting factor is the size of the address used for the slaves: 7-bit or bit, which support and devices, respectively.

Physically, there are two restrictions. First, the physical size of the bus because the bus is only meant for short runs the inter IC part. If the bus is too large there are capacitive loading and propagation delay effects that need to be dealt with. Second, some devices can't support the full range of I2C addresses. As examples, the MPU gyroscope only supports two addresses, and some devices reserve specific addresses for special purposes.

The maximum number of nodes is limited by the address space, and also by the total bus capacitance of pF, which restricts practical communication distances to a few meters. Addressing limits the number of devices- some can use bit addressing fairly rarely used , which limits the number of addresses to There are a handful of 'reserved' addresses.

That should be your primary reference document, not the various interpretations and subsets that exist elsewhere. See section 7. An i2c bus is limited mainly by the capacitance of the bus and thus speed , and accessible device addresses. And physical board space. But there is no real upper limit, when you factor in bus buffers, extenders, repeaters, hubs, multiplexers, switches or any other name for a device that can switch between multiple busses.

These add some i2c overhead, as may can be accessible via the same i2c bus. The PCAA for example, is an 8 bit bus switch.

And that's just with this device and not more. I2C specifies 2 address lengths, 7 and 10 bits , which gives a theoretical maximum of and distinct address, respectively. However, there are a few reserved addresses, such as 0x00 general call.

This further limits the address space. If you are building a system where you have direct control over the I2C devices, you can use the reserved addresses for your own use, but the system will no longer comply with the I2C standard. In addition to the addressing, there is the physical bus limitations. Each device on the bus needs to be able to pull the bus low in a certain time span depending on the bus speed.

If the bus has lots of capacitance, devices may not be able to pull SDA low fast enough, and the pulls ups may not bring SDA back up fast enough. Cypress PSOC chips have a bunch of software modules you can load into them to implement various functionality, and each piece of such software includes a datasheet, just as if it was a standalone chip.

It's glorious. In "Object-Oriented programming an evolutionary approach", Brad J. Cox the inventor of Objective-C hoped for the birth of "software-ICs", software components that should have been widely reusable, and documented with the equivalent of the datasheets used for traditional ICs. This was his vision for OOP. IC datasheets are dominated by the mundane but critical things like timing diagrams and electrical tolerances.

Software components can't even agree on which "ICs" fit into which breadboards. Be the change [pull request] you want to see in the World! I hate it when people say that!! Well, someone has to do the work. Asking someone else to do it seems kinda crappy if it's you who wants something for nothing. The problem I have is the sense "you're only allowed to ask for progress or give direction if you code it". Sure, no-one owes you their FOSS work, but it seems like we lose something if the only input allowed is from people able to do the coding.

Of course you might also just be a user. If you pay it forward, do you get to make a feature request?? If I don't code it myself Demanding work for free, and offering suggestions for improvements can be seen as synonymous, but they can actually be vastly different. Projects I use heavily, like Ubuntu, I try to make myself useful offering advice on forums.

That's not putting "money" in the bank of any coders but seems like it's in the spirit of FOSS - contributing what we can to create a better system.

There's always someone ready to exploit others. OJFord 7 months ago root parent prev next [—]. I think GP means they hate the phrase 'be the change you want to see in the world' as do I but was begrudgingly applying it to pull requests.

Read your comment after a whole day of desperately troubleshooting an i2c bus on way too long wires. I already held an mcp board in my hands thinking about how to retrofit every device with CAN, knowing this would take weeks until robustly running. Maybe adding LTC's will keep the system running until I truly have time for the conversion. Thanks a lot for your comment! Just created an account to write this! GeorgeTirebiter 7 months ago parent prev next [—].

That's right. A current source active instead of a 'poor man's current source' a resistor can help fix problems. I had to run kHz i2c over a few meters, and it really helps to drive the cables properly. Excellent recommendation, I'm going to test this out! It's very easy to remove the pull up resistors from most break out boards. The most likely issue you will encounter with trying to connect many I2C devices is address collisions where devices have fixed addresses or at least some fixed bits in the address.

This will probably limit you to about twenty or thirty useful devices on a bus. You can get around this with an I2C multiplexer[0]. It allows you to connect 8 devices to the multiplexer and then occupy one address on the main bud. How is the allocation of addresses done typically?

Are they always hardcoded? Is the same chip then available with different addresses different SKU? This might be as simple as one to three inputs which should be connected to ground or supply voltage to encode the last bits of the address. Other chips are a bit more creative, and allows you to, in addition to ground and supply, tie the address pins to the I2C clock and data pins. This allows it to generate four combinations from per address pin. People have already touched on setting the addresses using the pins but sometimes you can just buy near identical I2C parts that have slightly different part numbers because the range of user-selectable addresses is different.

For I2C addresses are hardcoded, with some chips leaving some bits to be set by hardware configuration. Far more interesting in that regard is the SMBus, that is compatible in most cases with I2C but can handle things like address resolution.

Typically addresses are only 7 bit 10 bit are possible but not all devices support that. I2c was conceived for communications between chips on the same board; it is extremely unlikely that one could fit that many chips on a board, all talking i2c with each other on the same bus. I2c switch chips also can be used to split the bus in multiple parts so that only a few chips at a time are physically connected to the bus. One person's unlikely is another person's design requirement.

Sometimes, there are obscure features and software but damn important i. MrBuddyCasino 7 months ago prev next [—]. This seems to only get into the electrical issues associated with connecting lots of devices to an I2C bus. Due to deficiencies in the protocol specifications and real-world implementation issues, there are logical problems as well.

If you're interested in the unpleasant details, whitequark has posted about this at length on Twitter. It's an absolute minefield of problems often subtle and hard to reproduce , and I go out of my way to avoid it if at all possible.

Hard to find any supporters of i2c these days. Complicates bus buffers; also complicates a bit-banging implementation. In the olden days, this was fairly easy by having an input on each pin, with the pull-down transistor per pin as shown in the article.

Being opinionated! Always hated breakout board producers for this pull-up resistor thing, especially since they are often targeted at the educational market. Why would you solder fixed pull-ups guaranteed to work only when it's just you in the bus and not even that as it's pretty common for uCs and SoCs to include their own pull ups? Teach your users the simple calculation needed to add pull-ups themselves! It's way easier to remove a pull-up resistor that's present and undesired than to add one that you don't have in your parts stash.

By the time you're doing that, you're probably reading someone's tutorial on how they did it and monkey-see, monkey-do, or you're far enough along in your learning journey to know to desolder some of the pull-ups. Arduino "won" by making things dead-easy to get working for people who frankly didn't have a clue what they were doing. This is a good thing, IMO. If it works straight away, you learn something and are inclined to take the second step. If the first attempt starts with a theoretically better lesson on how to calculate, select, order, and solder pull up resistors, you're failing at user engagement and unboxing experience by more than than you're gaining in theory-learning.

Partly agree, but it's not like you don't have to use resistors anywhere else with Arduino and the likes. Just to light up a LED you will need some and usually there are plenty included in starter kits. At least where I live there still are a couple of electronics retail shops where you can buy spare components. Also arguing that desoldering smd resistors is easier than finding a through hole one and plugging it into a breadboard or soldering into a prototype board is a bit of a stretch.

I've seen some other often more serious breakout producers to put solder jumpers in their boards to enable I2C pull-ups disabled by default. That's pretty nice since you can enable the I2C pull-ups just when needed. I have an "I2C" no clock wire necessary, but it's present bus with WS devices split evenly across a fan-out power and signal integrity multiplexer. This is because I couldn't get devices to maintain signal integrity only about , likely due to too much load on the bus or reflections.

Read data byte from CMPS03 7. Wait a moment That's almost it for simple I2C communications, but there is one more complication. When the master is reading from the slave, its the slave that places the data on the SDA line, but its the master that controls the clock. What if the slave is not ready to send the data! With devices such as EEPROMs this is not a problem, but when the slave device is actually a microprocessor with other things to do, it can be a problem.

The microprocessor on the slave device will need to go to an interrupt routine, save its working registers, find out what address the master wants to read from, get the data and place it in its transmission register. This can take many uS to happen, meanwhile the master is blissfully sending out clock pulses on the SCL line that the slave cannot respond to. This is called clock stretching. When the slave gets the read command from the master it holds the clock line low.

The microprocessor then gets the requested data, places it in the transmission register and releases the clock line allowing the pull-up resistor to finally pull it high. From the masters point of view, it will issue the first clock pulse of the read by making SCL high and then check to see if it really has gone high. If its still low then its the slave that holding it low and the master should wait until it goes high before continuing.

Luckily the hardware I2C ports on most microprocessors will handle this automatically. Sometimes however, the master I2C is just a collection of subroutines and there are a few implementations out there that completely ignore clock stretching. The result is that erroneous data is read from the slave.

Example Master Code This example shows how to implement a software I2C master, including clock stretching. It is suitable for controlling all of our I2C based robot modules. Since the SCL and SDA lines are open drain type, we use the tristate control register to control the output, keeping the output register low. This definition and the initialization is probably all you'll need to change for a different processor.

To initialize the ports set the output resisters to 0 and the tristate registers to 1 which disables the outputs and allows them to be pulled high by the resistors. This is nothing more than a subroutine call and return.

The following 4 functions provide the primitive start, stop, read and write sequences. All I2C transactions can be built up from these. Here's and example to start an SRF08 ranging in cm:. Internal register address will increment automatically. The definitive specs on the I2C bus can be found on the Philips website.

It currently here but if its moved you'll find it easily be googleing on "i2c bus specification". The store will not work correctly in the case when cookies are disabled.