TMS320F28388D: I2C in Free Data Format mode sends address anyway

Yaroslav Mudritsky

I've found a strange behaviour when i set I2C in Free Data Format .

Actually I want to write each byte and read each byte by myself, a complete control on I2C .

To accomplish this you can see this code:

Init

I2caRegs.I2CMDR.all &= ~(0x20U);
I2caRegs.I2CPSC.all = 0xB;        // Prescaler - need 7-12 Mhz on module clk
I2caRegs.I2CCLKL = 0x7;          // NOTE: must be non zero
I2caRegs.I2CCLKH = 0x8;           // NOTE: must be non zero
I2caRegs.I2CMDR.bit.MST = 0x1;
I2caRegs.I2CMDR.bit.TRX = 0x1;
I2caRegs.I2CCNT = I2C_NUMBYTES;
I2caRegs.I2CMDR.bit.BC = 0x0U;
I2caRegs.I2COAR.all = I2C_OwnAddress;      // Own address
I2caRegs.I2CSAR.all = I2CSlave_Address;      // Slave address
I2caRegs.I2CMDR.bit.FREE = 0x1;
I2caRegs.I2CSTR.all = 0xFFFF;
I2caRegs.I2CIER.all = 0x08;
I2caRegs.I2CMDR.all |= 0x0020;

Write DevAddress + 1b AddHI + 1bAddLO

I2caRegs.I2CSAR.all = 0x00;      // Slave address NOT USED
I2caRegs.I2CMDR.bit.MST = 0x1;
I2caRegs.I2CMDR.bit.TRX = 0x1;
I2caRegs.I2CMDR.bit.FDF = 0x1;
I2caRegs.I2CMDR.bit.NACKMOD = 0x0;
I2caRegs.I2CMDR.bit.STB = 0x0;

I2caRegs.I2CCNT = 3;            // DevAdd + 2bytes Address
I2caRegs.I2CMDR.bit.STT = 0x1;

I2caRegs.I2CDXR.all= 0xA0;
while(I2caRegs.I2CSTR.bit.BYTESENT != 0x1);
I2caRegs.I2CSTR.bit.BYTESENT = 0x1;

I2caRegs.I2CDXR.all= 0x00;
while(I2caRegs.I2CSTR.bit.BYTESENT != 0x1);
I2caRegs.I2CSTR.bit.BYTESENT = 0x1;

I2caRegs.I2CDXR.all= 0x01;
while(I2caRegs.I2CSTR.bit.BYTESENT != 0x1);
I2caRegs.I2CSTR.bit.BYTESENT = 0x1;

/*
I2caRegs.I2CMDR.bit.STP = 0x1;
while(I2caRegs.I2CMDR.bit.STP != 0x0);
I2caRegs.I2CSTR.bit.BYTESENT = 0x1;
*/

// HERE'S THE PROBLEM
//When I set next register SST I see that address inside I2caRegs.I2CSAR.all
//is sent on I2C , since I'm in FREE DATA FORMAT this should not happen
I2caRegs.I2CMDR.bit.STT = 0x1;  // SEND START CONDITION TO READ

I2caRegs.I2CCNT = 1;

I2caRegs.I2CDXR.all= 0xA1;
while(I2caRegs.I2CSTR.bit.BYTESENT != 0x1);
I2caRegs.I2CSTR.bit.BYTESENT = 0x1;

I2caRegs.I2CSAR.all = 0x00;
I2caRegs.I2CCNT = 5;
I2caRegs.I2CMDR.bit.TRX = 0x0;

count = 0;
while(count < 5)
{
    if(I2caRegs.I2CSTR.bit.RRDY ==0x1)
    {
        I2C_RXdata[count] = I2caRegs.I2CDRR.all;
        count++;
    }
}

I2caRegs.I2CMDR.bit.STP = 0x1;
while(I2caRegs.I2CMDR.bit.STP != 0x0);

I2caRegs.I2CSTR.bit.BYTESENT = 0x1;

I manually:

Set ByteCounter to 3 -> Set START CONDITION -> Send DevAdd -> Send AddHI + Send AddLOW ->

SET START CONDITION (HERE'S ERROR) -> Send DevAdd (R) -> Ask for n bytes

When I set the second StartCondition after address write, automatically I2C peripheral sends my registered slave address inside peripheral register (in this case 0x00) . This is an error since I must send this device address manually by application.

Here's what I see:

Why this is happening? What is wrong?

over 2 years ago

0 Manoj Santha Mohan over 2 years ago

TI__Guru 55700 points

When you send second start command, did you ensure i2c is in free data format

0 Yaroslav Mudritsky over 2 years ago in reply to Manoj Santha Mohan

Prodigy 130 points

Yes, is still in FDF mode. I've also tried to rewrite it before another StartCondition, but without changes.

Can you simulate this problem? It's strange that with FDF second StartCondition send address to target.

0 Joe Prushing over 2 years ago in reply to Yaroslav Mudritsky

TI__Genius 17081 points

Hi Yaroslav, I apologize for the delay in getting you a response. Unfortunately, Manoj is OOO and I'm not certain when he will return. I am working to track down another subject matter expert who may be able to pick up the support.

regards, Joe

0 Kevin Allen18 over 2 years ago in reply to Joe Prushing

TI__Mastermind 45606 points

Hi,

Are you certain it follows the value in I2CSAR? If you change it to 0x05 or something, does the STT byte match?

Can you try moving around the code below?

// HERE'S THE PROBLEM
//When I set next register SST I see that address inside I2caRegs.I2CSAR.all
//is sent on I2C , since I'm in FREE DATA FORMAT this should not happen

I2caRegs.I2CCNT = 1;

I2caRegs.I2CDXR.all= 0xA1;

// Move start condition until after I2CCNT and I2CDXR are set
I2caRegs.I2CMDR.bit.STT = 0x1;  // SEND START CONDITION TO READ

Best,

Kevin

0 Yaroslav Mudritsky over 2 years ago in reply to Kevin Allen18

Prodigy 130 points

Hello Kevin,

thanks for pickup my problem.

I've changed order as you proposed, first CNT, next DXR and than SST. But same behavior happens.

About address yes, when STT is called is printed address inside SAR.

Here's a screenshot of my register status before SST is called. I've changed SAR to 0x0022 and address byte after StartCondition of read part is 0x22 .

0 Omer Amir over 2 years ago in reply to Yaroslav Mudritsky

TI__Mastermind 30185 points

Hello Yaroslav,

Our primary expert is out-of-office, so I will look into this and get back to you sometime tomorrow.

Best regards,

Omer Amir

0 Omer Amir over 2 years ago in reply to Omer Amir

TI__Mastermind 30185 points

Hello Yaroslav,

You stated previously that you make sure you're in FDF before sending the second start condition, however based on your screenshot of the registers it looks like that's not the case. Can you please check your code and if needed, manually set the FDF bit?

Best regards,

Omer Amir

0 Yaroslav Mudritsky over 2 years ago in reply to Omer Amir

Prodigy 130 points

MDR is 0x4628 that is 100011000101000 . When is 1 is enabled.

0 Omer Amir over 2 years ago in reply to Yaroslav Mudritsky

TI__Mastermind 30185 points

Hello Yaroslav,

Apologies, I mis-read the register. I did not find anything in the TRM that directly explains this, so I will try to ask design team if there's any reason the I2CSAR register contents would be sent through the SDA line when using the repeated start in FDF mode.

Best regards,

Omer Amir

0 Omer Amir over 2 years ago in reply to Omer Amir

TI__Mastermind 30185 points

Hello Yaroslav,

The design team is currently looking into this now, they should have a response before the end of the week.

Best regards,

Omer Amir

0 Omer Amir over 2 years ago in reply to Omer Amir

TI__Mastermind 30185 points

Hello Yaroslav,

I have talked with the design experts and confirmed that there is an incorrect statement in the technical reference manual; the repeated start for I2C will always send an address. The peripheral does not support restart in FDF mode, it expects start, data, stop, and then a fresh transfer. I will file this fix for the manual.

Best regards,

Omer Amir

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TMS320F28388D: I2C in Free Data Format mode sends address anyway