I have a system with an I2C bus wired just like this:
Which one is better: put the termination pull-up resistor at the end of the connection (on the last board), or put the pull-up resistors on each slave board?
I'm having a problem in that initially it worked, but after some time the I2C communication to the board failed and can't be recovered (SCL always stuck low when I observe using a logic analyzer). On each board there's a chip like PCA9685, MCP3424, PCA9674, etc.
You can't just put a pull-up on every board: Your I²C devices need still to be able to pull down the lines, so if you increase the up-pulling by adding more boards, you're making it harder for the I²C devices to use the bus.
Then, adding more boards even without pull-ups on each of them will increase the capacitive load on the bus, up to a level where the bus might simply no longer work, because any one of your chips might no longer to pull down fast enough.
The solution to that is using either a more robust bus (CAN comes to mind), or redriving the bus every couple of boards. With I²C being a bidirectional bus, this is pretty complicated. A solution might be to limit the numbers of boards per bus to something benign (depending on your cable length and boards and chips), and then using a bus extender to drive multiple buses in what will look more like a star architecture than a daisy chain.
Consider having lower value pulldowns like 3.3k on the main board, and higher value ~22k resistors on the child boards. Not ideal, but better then one or the other.
As the previous answer noted, you will have an issue as your bus gets larger, with capacitance and eventually all the pulldowns.
You may have a situation where one of the devices wants to extend the bus cycle and another device does not like or support that. I will take a swag and assume the lowest resistance your weakest I2C device could drive is about 1.5K. Remember all the resistors on the bus are parallel are parallel. Treat each bus phase SDA and SDL separately when calculating the resistance. If that bus is longer than about 1 meter (yard) it will not be reliable but it is a great antenna for receiving electrical noise.
The I2C bus was not designed for inter module communication. I would seriously consider another method of running your bus, There are many but My favorite is to use Cory Fowlers CAN library for Arduinos, it does not take much code on your part to implement it. The MCP2515 module works very well, has the CAN controller and bus transceiver on it. You will need a SPI to communicate with it.
You can use CAN on other systems but you will need a different library. You can use CAN with a 3V3 or 5V system no additional voltages required.
