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Justplayin

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Joined: 31/01/2014
Location: United States
Posts: 313

Posted: 08:35am 17 Jun 2015

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I've just started playing around with I2C with the idea of transferring data back and forth between a Maximite and a Micromite. I can successfully transfer a 5 character string at 400K. At 200K and slower characters are lost. Scale up the 400K transfer to 10 characters and it starts dropping characters too. I am sure I am doing this all wrong since I have no idea what I'm doing. I would like to reliably transfer 128 bytes or more at a time.

Below is the two programs I'm testing with. The Maximite sends some characters to the Micromite. The Micromite receives the string and prints what is received then sends it back to the Maximite which prints the string. So... What am I doing wrong?

Maximite Master:

I2C OPEN 400, 500
k$ = "12345"
looper:
I2C WRITE &H26, 0, 5, k$
pause 50
I2C read &H26, 0, 5, j$
Print j$
j$=""
goto looper

Micromite Slave:

I2C SLAVE OPEN &H26, 0, 0, WriteD, ReadD
Do
WatchDog 1000
Loop

ReadD:
I2C SLAVE READ 5, msg$, recvd
x$ = msg$
Print x$;" "; Len(x$), recvd
IReturn

WriteD:
I2C SLAVE WRITE 5, x$
IReturn

Is there a bug in the SLAVE WRITE command? If I try to send a single character the program crashes with a message saying expecting a number. Two characters or more works fine.

--Curtis

I am not a Mad Scientist... It makes me happy inventing new ways to take over the world!!

Chris Roper
Senior Member

Joined: 19/05/2015
Location: South Africa
Posts: 280

Posted: 08:55am 17 Jun 2015

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If you have a PICKit Programmer you could use the Logic Tool to capture the Clock and Data signals during the transfer.

I have not tried it with the MicroMite yet but it has helped me debug I2C on other PIC32 applications in the past.

The PICKit logic tool is often overlooked but I personalty think it is worth buying a PICKit 2 for the Logic tool alone. That is why I keep mine even though I have an ICD3 for programming and debugging.

Cheers
Chris

http://caroper.blogspot.com/

Bizzie
Senior Member

Joined: 06/07/2014
Location: Australia
Posts: 185

Posted: 11:45am 17 Jun 2015

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See this post

Is almost the same problem, you need a pause after the I2C read.

Rob White

Justplayin

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Joined: 31/01/2014
Location: United States
Posts: 313

Posted: 12:36pm 17 Jun 2015

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Bizzie said Is almost the same problem, you need a pause after the I2C read.

I tried adding pauses after every read and write... same results. Increased values until the watchdog kicked in then I upped the watchdog time too.

--Curtis

I am not a Mad Scientist... It makes me happy inventing new ways to take over the world!!

Justplayin

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Joined: 31/01/2014
Location: United States
Posts: 313

Posted: 01:29pm 17 Jun 2015

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Hey Rob, after looking through the thread again I came to a conclusion... Duh! The pause works better BEFORE the read to give the data time to arrive. I kept putting the pauses after. Things are now working much better, but I have a lot more testing to do.

--Curtis

I am not a Mad Scientist... It makes me happy inventing new ways to take over the world!!

Grogster

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9078

Posted: 02:44pm 17 Jun 2015

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I realise you have pretty much settled this issue down, but I have always has isses with sending long strings with the I2C. SHORT strings are no problem, but if you are trying to send long strings like you are, I found that byte-at-a-time with acknowledge works exteremely well, with zero dropped characters, and pretty respectible speed.

This is how I am doing it:

I2C MASTER:

DTA$=L1$+L2$+L3$+L4$+L5$+Chr$(250)
P=1

I2C open 100,100

Timer=0
Do
BYTE=Asc(Mid$(DTA$,P,1))
I2C write &B1010101,0,1,BYTE 'Transmit byte
I2C read &B1010101,0,1,BUF 'Wait for acknowledge byte
P=P+1
Loop Until BYTE=250

Print "Done. (";Timer;")"

End

The master code sends one byte at a time, and waits for the slave to acknowledge.
This byte can be anything really, but I chose 250 decimal. This EOM(End Of Message) byte must be added to the end of the string to send as in the example above. In this example, L1$-L5$ were just lines of text, and they are added together to make one big string for the purposes of testing.

I2C SLAVE:

TESTI2C:
Flag=0
Open "com1:19200" As #1
Open "com2:2400" As #2

I2C SLAVE OPEN &B1010101,0,0,I2C_OUT,I2C_IN
Print "Waiting for I2C data..."

Do
If BITE=250 Then
Print DTA$
DTA$="":BITE=0:B=0
EndIf
Loop

I2C_OUT:
I2C SLAVE WRITE 1,75 'Send K acknowledge byte
IReturn

I2C_IN:
I2C SLAVE READ 1,BITE,BUF
DTA$=DTA$+Chr$(BITE)
B=B+1
IReturn

End

The slave code sends a "K" for every character it receives from the master, and the master WAITS till it gets this "K" back from the slave before it tries to send another byte to the slave. This goes around in circles until the EOM, at which point the main loop picks up on that and prints out the message.

This was just for testing purposes, and was further expanded to suit my purposes, but this method seems to work flawlessly for long strings - I have not been able to find any errors in data during my testing, and yes - also runs at 400kHz.(provided your I2C interconnecting is done correctly)

Smoke makes things work. When the smoke gets out, it stops!

Justplayin

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Joined: 31/01/2014
Location: United States
Posts: 313

Posted: 04:39pm 17 Jun 2015

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Thanks Grogster,

I'll have to wait and take a look at your code tomorrow... It's getting late here.

--Curtis

I am not a Mad Scientist... It makes me happy inventing new ways to take over the world!!

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