I2C communication between PIC16F877a and Raspberry pi 3

Hi,

This is a bit of an ambitious first project. i2c communications is not very easy: Although the protocol allows the slave (your PIC in this case) to slow down communications from the master (the PI in this case), the hardware on the PI has a bug that makes this unreliable.

So in practice, the pic will have to be VERY fast, to be sure that it won't slow down communication with the pi to work around the bug.

I would recommend that you use the UART to communicate with the PIC.

It is reasonably easy to have something like:

if (character_available () ) {

   character = get_character ();

   if (character == '\n') { 

      process_command (buffer);

      pos = 0;

   }  else {

     print_character (character);

     buffer[pos++] = character;

   }

So now your PIC can accept commands from the pi. You can use a terminal program like minicom to communicate with your PIC. This allows for easy debugging as well.

Just like i2c, this requires you to hook up two data-wires between the pi and the PIC. (besides power and ground).

I worked with PIC microcontrollers early this century, but I've switched to other microcontrollers since then. So I'm not familiar with the PIC specific details. But I do know stuff about PI, I2C and microcontrollers in general.

(The example code above is slightly too simple: For example, you'll quickly appreciate adding something like:

if ((pos > 0) && (character == DELETE)) {     pos--;

     print_string ("\b \b");

  }

Alex,

Sometimes there can be a single bit set incorrectly in one register you've never noticed from the data sheet !

You didn't say what tools you are using for the PIC development; I'm assuming you are using the Microchip MPLAB X IDE and XC8 compiler (both free to download from Microchip's site). If you are, then an additional step that helps get things up and running is to use Microchip's MPLAB Code Configurator (MCC) which gives a nice GUI for selecting options on each peripheral (I2C, SPI, UART etc) and then will generate the code for you. My only caveat is that it isn't always the best behaved add on for Netbeans (which MPLAB X is written for) but MCC does normally get those obscure registers setup correctly so that the peripheral is at least running.

Another intermediate step to getting your project working is to perhaps use an Arduino. They have many easy to copy examples using I2C - use it to prod the other device or to listen for data (which can then be displayed via its inbuilt terminal).

If you could post any circuit diagram (sketch or clear photo) and code that might help someone in the community spot what is up.

Rod

@14rhb Microcontrocontrollers (PIC, AVR, arduino, STM32) like the pi, are often used as the MASTER in an i2c bus situation..... An arduino might for example, control a few relays based on a pressure sensor, or use a 9DOF sensor to control two motors to balance a robot. Anyway, the arduino is then a MASTER towards those sensors, and the code/libraries for that is well-used, well-debugged and well-documented. But the "arduino is an I2C slave" is not often used. I'm not even sure a library exists.

Is that phenonenon perhaps just how many home/maker projects are designed: where the Arduino is the 'intelligent' part on the I2C (eg Master) whilst servos, temperature sensors etc are the I2C slaves? You should be able to use the Arduino Wire.h library to configure the Arduino as a slave like in this article here by Nick Gammon.

Rod

But the "arduino is an I2C slave" is not often used.

May be of interest/maybe not (as it is drifting off-topic), but that's pretty much how the GrovePi is configured.

https://www.dexterindustries.com/grovepi-tutorials-documentation/

It's an ATmega 328P microcontroller stacked on top of a R-Pi Master and configured as an I2C slave to pass the sensor data back to the R-Pi:

https://www.dexterindustries.com/GrovePi/engineering/software-architecture/

Drifting a bit off-topic from the original post, but here is an example project with 20x Arduino Nano's being slaved off an Arduino Nano master via the I2C bus.

https://www.youtube.com/watch?v=ypBI0wJYfcQ

(In addition there are also 5x Arduino Uno's with MP3 player shields and a 6th Uno with a DMX shield but not sure how they communicate with the master Nano.)

It's a rather large installation at Carnegie Science Centre

Carnegie Science Center: Home

There are a couple of write-ups on Adafruit:

https://blog.adafruit.com/2018/03/05/200-button-wall-with-light-sound-and-interactive-effects-also-a-tour-of-the-project…

and Hackster:

https://blog.hackster.io/this-200-button-effects-wall-will-satisfy-your-button-mashing-compulsions-a839f13a874a

May be of interest to some in using the I2C bus for microcontroller-to-microcontroller communications.