PIC to PIC over I2C – Default Examples

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PIC to PIC over I2C – Default Examples

Post by viki2000 »

I was looking at next example:
http://www.matrixtsl.com/mmforums/viewt ... ave#p17145
but is old and then I noticed next I2C Slave help examples:
https://www.matrixtsl.com/wikiv7/index. ... 3e364f2eff
I took the 1st case with
„The slave device is connected to a bank of switches, the master device to a bank of LEDs. The value of the switches is passed to the master LEDs.„
I did not test with real PICs, because I do not have now PIC16F1937.
If necessary I can use real PICs, other than PIC16F1937, for example PIC16F1825 or PIC16F1827 or PIC16F1829.
But I have tried in Proteus with PIC16F1937 and the code from help files above does not work for me.

Questions:
1) Did you try that code with FC7? Is it working indeed?
2) Can you help to debug it?
3) Is it possible to provide an example where instead of “cal_i2c1” component to use I2C Master and I2C Slave?
http://www.matrixtsl.com/blog/simplifie ... c-and-spi/

Proteus schematic:
https://ibb.co/mbTHu5

Code:
PIC16F1937_I2C_Master_Read.fcfx
Master Read I2C
(9.39 KiB) Downloaded 502 times
PIC16F1937_I2C_Slave_switches.fcfx
Slave Switches I2C
(11.48 KiB) Downloaded 535 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

So I understand that no one up to now tested the provided examples with PIC16F1937 from next Flowcode Wiki page:
https://www.matrixtsl.com/wikiv7/index. ... 3e364f2eff

I do not have PIC16F1937, but I found some PIC18F4550 around and I decided to adapt the examples and test them also with real devices, besides Proteus simulation.
In case would not work for me, then I will startup from some other working/tested examples, even if they are not written with Flowcode.

I2C projects helpful links:
https://electrosome.com/i2c-pic-microco ... mplab-xc8/
http://hades.mech.northwestern.edu/inde ... tween_PICs
http://botdream.com/oldsite/blog/2008/0 ... index.html
http://www.8051projects.net/wiki/I2C_Im ... ion_on_PIC

http://ww1.microchip.com/downloads/en/A ... 00736a.pdf
http://ww1.microchip.com/downloads/en/a ... 00735a.pdf

In mean time would be helpful any suggestion why the provided examples do not work or at least to know if someone else tried/tested them with successful results.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

One error detected in the Wiki Examples files:
https://www.matrixtsl.com/wikiv7/index. ... 3e364f2eff
At "Slave Switches Example" in the above link there is Atmega set instead of PIC16F1937:
error1
error1
I2C_PIC16F1937_error1.jpg (72.24 KiB) Viewed 20785 times

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

Hi
Thanks for the spot.
I do know that the I2C Master/Slave examples do work with at least the 16F1937 and Arduino Uno,
they were tested on those products at the time the originals were written.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

I just ordered some 16F1937.
I will test those examples with real devices during the next days and I will let you know the results.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Hi,
I have received some PIC16F1937 chips and I made a test today.
1st error: the frequency was not set properly in the Project Options in the provided examples and no OSCCON in C block included in the code.
I decided for internal oscillator at 16MHz, and then the OSCCON must be initialized. I did it with 0x7A and I measured one pin on/off 1ms to see if the clock was good. The clock is fine with OSCCON=0x7A; and internal oscillator at 16MHz.
With all these, the provided code for I2C does not work.
The test was performed using a breadboard as in photo below and I captured the I2C signals with a DSO that has I2C decode function.
Besides that I have tried the same code by simulation the project in Proteus. The virtual oscilloscope in Proteus shows the same signals as the real oscilloscope. That proves that is nothing wrong with the hardware/connections and it is only a problem of code, how the I2C is setup to work.
With these being said, I consider the provided examples from Flowcode Wiki Help not functional and not tested.

Could you debug them and make them functional and test them with real devices?
I2C_Breadboard.jpg
I2C_Breadboard.jpg (161.1 KiB) Viewed 20731 times
I2C_Debug_Real Oscilloscope.png
(26.41 KiB) Downloaded 11514 times
I2C_Debug_Proteus.jpg
I2C_Debug_Proteus.jpg (267.44 KiB) Viewed 20731 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Here is the non-working code used in the above tests:
PIC16F1937_I2C_Master_Read2.fcfx
(9.52 KiB) Downloaded 412 times
PIC16F1937_I2C_Slave_switches2.fcfx
(11.6 KiB) Downloaded 413 times

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

Well, that is very odd.
Your code works for me on hardware.
I even changed the Slave so that instead of reading switches, it increments "Data" each time round the loop, and I got counting LED outputs on the Master.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

What hardware do you use? Can I see a photo with it?
Can you make some oscilloscope screenshots with the I2C transactions as I have posted above?
Did you really use my .fcfx file above or did you modify a bit the code?
Could you please upload here the exactly .fcfx files that works for you?

I will try to debug more, but I2C is not always easy. Any suggestion for I2C debugging is appreciated.

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

Hi,
I used exactly the same Master, the Slave I changed the switch port to match my hardware (2x EB006)
Modified Slave attached.
Maybe try disabling the port read, and enable the "Data = Data + 1" icon as see if you get the counter on Master LEDs
Leigh

edit: I used 3K3 pull-up resistors, I think you have 4K7, but I doubt that makes the difference
Attachments
PIC16F1937_I2C_Slave_switches2 counter.fcfx
(11.78 KiB) Downloaded 281 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Here are my thoughts for today:
- If we use the same .fcfx code and works for you, but not for me, then is a hardware problem.
- I do not have any EB006 boards, but looking on internet I noticed are different versions. What version are yours?
- The resistors 4.7K or 3.3K should have influence only on rise edge and I did not notice anything wrong, anyway I can try with 3.3K tomorrow.
- Let’s suppose my hardware has a problem, some missing connections or a wrong setting somehow, I will check that one more time tomorrow and I can make the electrical diagram 1:1 that matches the breadboard setup, but then how come the Proteus simulation does not work either and shows the same waveforms as the real oscilloscope? That’s my biggest question which leads to the last question for you.
- Would be possible, for I don’t what kind of reason that the provided code examples work only with EB006 hardware?

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

My EB006 are version 9, but I don't think version will be a factor.
From your oscilloscope it would appear that the Master is working, but not the Slave.
What about connecting both Vdd/Vcc pairs?
The Slave program has a toggle of Port C pin 0, does that happen on your hardware?
Can you try the Data count modification and remove the switch read, just to eliminate any issues there?
Could you post your .hex files, and matching .fcfx, and I will check against my builds.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

I was thinking at the PICs.
Can you tell me what Revision ID have your PIC16F1937?
I checked the Silicone Errata, but on MSSP block seem only SPI affected:
http://ww1.microchip.com/downloads/en/D ... 00479M.pdf
My PIC16F1937 chips are new chips with ID Revision 9, checked with MPLABX+Pickit 3.
If the chips would be the problem, then how come the simulation with Proteus give the same errors/I2C waveform signals? On the other hand, it woul be possible that some bits/registers might not be simulated properly with Proteus, it is known for that for some other chips, but then normally it tells you which are not emulated.
I will come with more info and answers to your questions during the next days.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Hi,
As promised, I have made the circuit diagram/schematic of the real circuit that I have used on breadboard tests.
To emulate as close as possible the real breadboard, I have use Fritzing (http://fritzing.org/home/ ), because is free and another program as Virtual Breadboard (http://www.virtualbreadboard.com/ ) seems nice, but is not free.
Below are the breadboard and schematic as pictures and the Fritzing project.
Because the default LED Bar graph has 10 positions and I did not spent time to modify that component for 6 positions as I have in reality, I just connect fewer positions, in fact 5 positions, because another component, the resistor pack (array) was with 5 positions. The same with dipswitches component, has 8 positions and I have used only 5, to correspond with 5 resistors and 5 LEDs. In reality I use 5V stabilized power adapter, not batteries.
I2C PIC16F1937_1_bb.png
(186.31 KiB) Downloaded 11442 times
I2C PIC16F1937_1_schem.png
(78.54 KiB) Downloaded 11442 times
I2C PIC16F1937_1.zip
(32.9 KiB) Downloaded 259 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Then I have made the electrical diagram below in a photo editor, which reflects better the connection from real breadboard.
Here we may object to the missing pullup resistors to 5V on the dip-switches, so when the switches are opened, then the inputs are in an uncertain state. But we can enable the pull-up resistors on PORTB with a C code.
Nevertheless, if the states would be uncertain and oscillate, then I should see the LEDs also oscillation on/off. If I close the switches, then the inputs are connected to GND with 0 logic state. Even in this case the LEDs on the Master are on all the time, indicating that I2C is not working.
If we look at the oscilloscope screenshot above, then we see indeed that is a problem with the Slave. The Start initiated by Master is present, the 7bits of the Slave Address is sent by Master, the 8th bit R/nW bit is 0 indicating a Write operation, but the 9th bit which is Acknowledge and comes from Slave is 1, meaning NACK (not acknowledge), so the slave does not respond.

Can you tell me what Revision ID have your PIC16F1937 chips?
I will try now what you suggested.
I2C PIC16F1937.jpg
I2C PIC16F1937.jpg (119.11 KiB) Viewed 20659 times

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

Thanks for the further info.
The 8th bit is set high to indicate a read, so as you confirm, the Master is correct.
The 16F1937s I have here are a few years old, I've not had chance yet to investigate the revision

If you could try an incrementing Data byte, and if send your .fcfx and .hex files I will check that we are compiling to the same code.

edit: I've attached my Slave hex that has the Data counter.
Attachments
PIC16F1937_I2C_Slave_switches2 counter.hex
(1 KiB) Downloaded 183 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Here is a short update, it seems I arrived somewhere.
I followed your suggestions: I connected both Vdd/Vcc, then I changed the MCLR resistors to 10K and pull-up resistors to 3.3K. But I think these did not make any changes.
Then I tried your proposed code “PIC16F1937_I2C_Slave_switches2 counter.fcfx” by disabling PORTB read (did not read anymore the switches) and the LEDs started to work showing/changing the numbers in binary format.
I checked the I2C bus with the oscilloscope and it looks good now, I have the ACK bit from Slave. Maybe I will post some screenshots during the next days.
It seems the reading of the switches is the problem, in my case PORTB.
I can assume for the moment only next possible failures:
- Missing pull-up resistors and uncertain state for inputs. By the way how do we enable with C code the pull-up resistors on PORTB?
- Bad hardware connection: the PICs are in socket and the socket inserted on breadboard, the dipswitch is on PCB and some pins soldered on PCB to be able to insert it in breadboard. I will check one more time tomorrow the entire PORTB connections and eventually I will test other small switches with extern pull-up resistors soldered to them.
- Maybe I will try another breadboard type.
- The Proteus simulation does not work, not even now with the Data counter code mentioned above, cannot simulate the working hardware, maybe there is a limitation with the emulation of the PIC16F1937 chips, but let’s forget about it for the time being and I will focus on real device.
I will bring more info tomorrow.

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Re: PIC to PIC over I2C – Default Examples

Post by Benj »

By the way how do we enable with C code the pull-up resistors on PORTB?
The following C code will enable the internal weak pull up resistors for all PortB pins on the 16F1937 device.

Code: Select all

OPTION_REG &= 0x7F;
WPUB = 0xFF;

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

The circuit works now.
The last problem was related with pull-up resistors on PORTB, because I did not use any external resistors attached to the dipswitches.
It works also if I use 4.7K resistors for MCLR instead of 10K and if I use 4.7K resistors of I2C resistors instead of 3.3K. It works also if I use the VDD/VCC connections on only 1 side of the PIC16F1937.
To recap, the problems were as following: Atmega MCU instead of PIC16F1937, then OSCCON=0x7A; - mistakes on the given original examples and the last one, my mistake, pull-up resistors on PORTB.
PIC16F1937 allows setting individual pull-up resistor on each pin of PORTB.
Because I do no use a dipswitch with 8 positions, but only with 6, connected to the pins RB7-RB2, then I set up the pull-up resistors on PORTB only for RB2-RB7, so instead of WPUB=0b11111111=0xFF, I used WPUB=0b11111100=0xFC;
Here is a photo with the working circuit on breadboard:
I2C PIC16F1937_breadboard_good.JPG
I2C PIC16F1937_breadboard_good.JPG (134.54 KiB) Viewed 20629 times
Here is the oscilloscope screenshot with I2C bus working signals:
I2C_good.png
(201.74 KiB) Downloaded 11412 times
Here are explanations to the above oscilloscope screenshot with I2C bus working signals:
I2C_good_explanations.png
(312.17 KiB) Downloaded 11412 times
These explanations may help to debug I2C:
- The Master always starts and stops the communication. The Master is the only one providing the clock.
- The Slave can also control the SCL/SDA lines.
- It may be clock stretch situations, when if the Master is too fast with the clock, then the Slave tells to slow done the clock, otherwise no communication can take place.
- I find next file very good: http://opensat.cc/wiki/_media/ko:contri ... oscope.pdf
Particularly to the above oscilloscope screenshot:
- The Master initiates the communication (Start) with the falling edge of the SDA while the SCL is HIGH.
- The it follows 9bits, from which 8bits are Slave Address 0x54 combined with a Read operation (R=1, which is the 8bit, because is a 7bit address), so we have 0x54 bitwise OR 0x1 = 0x55.
- The next bit is Acknowledge bit sent by Slave, saying that received the correct address and info that the Master wants to Read.
- Then follows 8bits of Data sent by the Slave.
- At the end of Data bits, the Master sent Not Acknowledge as indication that received the requested 1byte of data.
- In the end the Master closes the communication (Stop) with the raising edge of SDA while SCL is HIGH.

Now everything works fine, but still remain 2 open questions:
- My initial 3):
Is it possible to provide an example where instead of “cal_i2c1” component to use I2C Master and I2C Slave?
http://www.matrixtsl.com/blog/simplifie ... c-and-spi/
- Right now the Slave code checks for the Slave status continuously in a While loop.
- Most of the XC8 examples from Microchip use the MSSP interrupt.
Could you change the code to use MSSP interrupts, so the Slave to be free to do something else and to not be busy in that While loop?

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Here are the working codes used in the above test:
PIC16F1937_I2C_Master_Read_good.fcfx
(9.52 KiB) Downloaded 242 times
PIC16F1937_I2C_Slave_switches_good.fcfx
(11.66 KiB) Downloaded 239 times
Looking at the last breadboard photo above:
- The Master is on the left side and has LEDs attached to the PORTB:
- The Slave is on the right side and has dip-switches attached to the PORTB.

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Now that the first example works, I decided to try the 2nd example:
“The slave device is connected to a bank of LEDs, the master device to a bank of switches. The value of the switches is passed to the slave LEDs”
from Wiki Help page:
https://www.matrixtsl.com/wikiv7/index. ... 3e364f2eff
And again does not work.
I have used the same hardware/breadboard/schematic as above for the 1st example, only that I changed the function of the microcontrollers:
- The Master is on the right side and has dip-switches attached to the PORTB.
- The Slave is on the left side and has LEDs attached to the PORTB.
I only have added the OSCCON and the register with pull-up resistors, but it does not work.
Then I have tried the trick with Data counter without reading PORTB with switches.
Still it does not work. Actually I cannot see any I2C signals with the oscilloscope.
The non-working codes used are:
2._I2C_Master_Switches.fcfx
(10.14 KiB) Downloaded 196 times
2._I2C_Slave_LEDs.fcfx
(10.55 KiB) Downloaded 199 times
Could you help to test/debug this one too?

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

Today in the morning I solved the problem.
For debugging I have done next:
- Removed the Salve chip and I noticed with the oscilloscope that the Master is sending continuously I2C signals SCL and SDA as address, but no ACK from Slave.
- The communication works one time at power on moment, after which the SCL and SDA were low.
I supposed the problem comes from Slave by not sending regularly the ACK signal, most probably because the buffer was not empty. In the Slave code, when we test the Status for Data received, on the No branch I have added one more reading instruction with a "junk" unused byte only to empty the MSSP buffer. Then everything worked fine.
Here are the working flowcharts:
PIC16F1937_I2C_Master_Write_Switches_good.fcfx
(10.14 KiB) Downloaded 222 times
PIC16F1937_I2C_Slave_LEDs_good.fcfx
(10.93 KiB) Downloaded 211 times
And the oscilloscope screenshot I2C bus working signals:
I2C_good_Master_Write.png
(257.18 KiB) Downloaded 11344 times

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Re: PIC to PIC over I2C – Default Examples

Post by viki2000 »

For who is interested, I have tried also PIC18F4550 on the same breadboard and works, of course with a bit different settings for ports, register for pull-up resistors and oscillator.
This time I used an external crystal 16MHz and with internal PLL I have 48MHz clock for CPU.
I use PORTB to read the switches and PORTA for LEDs.
Here is the breadboard setup with PIC18F4550 on top and previous PIC16F1937 at the bottom:
Full breadboard.JPG
Full breadboard.JPG (154.72 KiB) Viewed 20541 times
PIC18F4550_I2C.JPG
PIC18F4550_I2C.JPG (172.49 KiB) Viewed 20541 times
Here is the code used for both situations:
PIC18F4550_I2C.zip
(10.51 KiB) Downloaded 275 times
2 more observations:
- The component I2C CAL seems that works only with hardware Channel of I2C. When I set it Software, then it does not work. The ACK signal is not returned from Slave after the first 8bits with address + R/W.
I don’t really know why, but I guess due to the explanations from Wiki Help page of the “Component: I2C (Peripheral CAL)”:
http://www.matrixtsl.com/wikiv7/index.p ... 43fd1147ca
which at Property Reference has written:
“Channel
This property is of type Fixed list of ints and can be referenced with the variable name CHANNEL.
Channel selection”
- All these codes, I mean the .hex result, were tried also in Proteus simulator: for PIC16F1937 and also for PIC18F4550 and do not work. Something is not emulated proper, because in reality they work and it is not a complicated circuit.
Who can find a solution for Proteus based on the above codes is welcome to post it here.

From my point of view in order to complete this topic, regarding the I2C communications between 2x PICs, it remains to find 2 more solutions, as I mentioned in some posts above:
1) My initial 3), to make it work with I2C Master and I2C Slave instead of “cal_i2c1”
http://www.matrixtsl.com/blog/simplifie ... c-and-spi/
2) To implement the code using the MSSP interrupt, so the Slave to be free to do something else and to not be busy in that While loop, similar, but perhaps/hopefully simpler as was done here:
http://www.matrixtsl.com/mmforums/viewt ... ave#p17145

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Re: PIC to PIC over I2C – Default Examples

Post by LeighM »

Hi,
Thanks for all your notes.

It's worth noting that you can do other processing in the loop with the test for the status change.
The status is read from the hardware peripheral register, so it cannot be missed whilst doing other processing.
This the reason why the Slave is only available in hardware mode, not software.
Although this could probably be done via an interrupt on change port, but that would be a further complication to the Slave implementation, so we avoided that. As with most components, it's creating something generic enough to work across differing platforms that can cause restrictions on what we would like to do.
I'll try to have a look some time at adding an interrupt based example.
Leigh

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Re: PIC to PIC over I2C – Default Examples

Post by Docara »

Hi Leigh,

Further to all the work you and viki2000 have done here, can I take from it that the I2C routines in FC are stable to use as long as they are based on hardware? And therefore can be used across all owned chip pack devises where applicable?

Secondly, did you ever sort out an interrupt based routine as mentioned in your last post here

Thanks
Matt

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