2 Arduino I2C communication

[chipfryer27]

Hi

Ages ago I was trying to get a PIC talking to (I believe) a 328P and could send from PIC (Master) without issue but if I remember correctly I was getting similar in that the slave wasn't returning the correct info. Can't recall exactly the issue, but I had to move on to something else before I could figure it out.

Regards

[max.tisc]

I activated the LED on port B7 at the end of reception and the LED turns on and off quickly, but I only get one sequence, maybe a bug?

[mnfisher]

It is very odd = what hardware are you testing on? As you can see from my screenshot it had counted up quite a few iterations when I took it?

Can you 'disable' the 'Read' in the sender (master - will perhaps have to think again about the naming!)

Iain - can you remember what you got returned by the 'read' - I just get the first byte (which is correct) repeated however many times

I had a little peek at the CAL code and it all looked okay - and it seems to work receiving from sensors etc - maybe have some time for a better look at the weekend.

Martin

[mnfisher]

Looking at your screenshot - after the 'receive' SDA stays low which holds the i2c bus as 'busy' - and prevents further transmission.

If you look at the trace I posted - you can see that SDA goes high again after the 'read'
It might be a slightly different board - could you try a pull-up resistor on the SDA and SCL lines (4k7 or 10k) and see if that does anything beneficial?

Martin

[mnfisher]

Another 'oddity' - when writing m->s there is an ~18us delay between bytes. On receiving s->m there is a much shorter 'gap' (~8us) and adding a delay after each byte is transmitted doesn't affect this as expected - adding a 1ms delay gives 2 bytes with first value (and a 8us delay between them) then after ~1ms 2 bytes reflecting the 2nd byte of the reply (again with a short delay between them)
A 100us delay gives a similar result but with a 27us delay between the pairs.
As though the receiver isn't waiting for the data to become available correctly?
Adding a delay before the reply does result in a delay however - with the data received as above

Martin

[max.tisc]

you were right, the pull-up resistors were missing, I put them at 5.6k and now the data arrives every 100ms.
if it helps I already used a DS3231 which communicated with the Arduino in I2C and I could read and write on it, maybe the solution is there

for chipfryer27 if you remember what you did to solve it would be great

thank you all

[mnfisher]

Another step forward

The RTC is acting as a slave device. Could maybe look at the output for this and see what/how it varies?

[max.tisc]

ok I'll try to do something tomorrow

[chipfryer27]

Hi

It was last year (or before) so my memory of it isn't great and I thought it was something I'd done wrong. Reading this post did sound familiar though and I think it was not refreshing the data to be returned. I'd need to go dig out the project file though.

Sorry I can't be much help,

Regards

[mnfisher]

A bit more playing and I almost got it to work by tweaking the CAL_I2C file - but it would work for one time and then stop. After a bit more fiddling - no joy.

So - I rewrote the slave side using the TWI interrupt to handle receipt and sending of data. This worked remarkably easily - so here is a very simple 'proof of concept' - it receives data (and stuffs it into a circular buffer) and serves up data (an incrementing counter) when requested.

Needs some work to make it truly useful - but should be easy to modify. The 'main' just initialises the i2c and enables the interrupt handler - there is nothing for it to do after that

i2c_rcv3.fcfx

(11.89 KiB) Downloaded 548 times

Used with previous 'master' - receives and then sends 4 bytes... (and works with any number as requested or transmitted by the master)

Martin