CCS/TMS320F28075: I2c Stop Condition not occurring and first bit missing in data sent

Lakshmi Tejas M A

Part Number: TMS320F28075
Other Parts Discussed in Thread: DAC7574, CONTROLSUITE

Tool/software: Code Composer Studio

Hi all,

I am trying to test the I2C module of TMS320F28075, I am using the sample code of control suit which is written to eeprom v180. I have not connected any eeprom but i have connected both SDA and SCL to Vcc- 5V via a resister 3KΩ. Like this in the image.

But when i go to debug session, I see a start condition happening and Data is being sent (address only), 8 bit mode is being used, thereafter 8 bits(address) are generated but no stop condition is happening. BTW if address bytes sent is 0x98(10011000) the SDA refelects with (00110000) ie,

if 10101010(0xAA) is sent i am seeing 01010100 means left shifted data is being sent on SDA.

I have loaded the snap for reference too.

Image: sent address is 0xAA

Channel 1 : SDA

Channel 2 : SCL

I have initiated I2C like this

I2caRegs.I2CSAR.all = 0x0098;

I2caRegs.I2CPSC.all = 6;
I2caRegs.I2CCLKL = 10;
I2caRegs.I2CCLKH = 5; 49k
I2caRegs.I2CIER.all = 0x24;

I2caRegs.I2CMDR.all = 0x0020;

I2caRegs.I2CFFTX.all = 0x6000;

Write operation

if (I2caRegs.I2CMDR.bit.STP != 1){

I2caRegs.I2CSAR.all = 0x98;

if (I2caRegs.I2CSTR.bit.BB == 1)
{
return I2C_BUS_BUSY_ERROR;
}

I2caRegs.I2CCNT = 1;

I2caRegs.I2CDXR.all = 0xAA;

I2caRegs.I2CMDR.all =0x6E20;

}

Can any one tell me what might be missing or issue is?

Thanks in Advance

over 6 years ago

0 Sean Bigley over 6 years ago

TI__Genius 17175 points

Hi Lakshmi,

I'm writing to let you know that a C2000 team member has been assigned to this post and should be answering shortly.

Sean

0 Lakshmi Tejas M A over 6 years ago in reply to Sean Bigley

Intellectual 370 points

Hi Sean,

Thank you for assigning a C2000 member to answer it, I am eagerly waiting for the reply.

Regards,
LT

0 Manoj Santha Mohan over 6 years ago

TI__Guru 55700 points

Lakshmi,

Based on your I2C configuration, you are using 7-bit addressing mode.

In 7-bit addressing mode, with I2CSAR = 0x0098, Bit0:6 represents the 7 bit slave address. You would see 0x30 in waveform

Your SDA pin is pulled, that indicates that you are seeing a STOP bit.

Regards,
Manoj

0 Lakshmi Tejas M A over 6 years ago in reply to Manoj Santha Mohan

Intellectual 370 points

Hi Manoj,

Thank you for the reply, As you said I see 0x30 in the waveform. but actually I should get 0x98 right?

You said SDA is pulled high, yes it is pulled high but not during the high level of SCL. For stop condition SDA must be pulled high during the high level of SCL.

Image source: 28075 I2C module documentation

What i am getting is like this.

Regards,

0 Manoj Santha Mohan over 6 years ago in reply to Lakshmi Tejas M A

TI__Guru 55700 points

No, you will not see 0x98 just because you wrote 0x98 in I2CSAR. Bit7 is ignored as only Bits0:6 represents address in 7 bit addressing mode. That is the reason why you observe 0x30 after start bit.

Regards,
Manoj

0 Lakshmi Tejas M A over 6 years ago in reply to Manoj Santha Mohan

Intellectual 370 points

Hi, Manoj

So if the SDA sends 0x30 instead of 0x98 then will the Slave be able to detect the address as it is being called? I am using a DAC7574 evm with address 0x98. I am asking this because i am not able to see any ACK occurring when I have connected the DAC7574 with A1A0 = 00.

Regards,
LT

0 Manoj Santha Mohan over 6 years ago in reply to Lakshmi Tejas M A

TI__Guru 55700 points

Lakshmi,

For DAC7574, if you have A0 = A1 = 0, your slave address is 0x4C and not 0x98

Regards,

Manoj

0 Lakshmi Tejas M A over 6 years ago in reply to Manoj Santha Mohan

Intellectual 370 points

Hi Manoj,

I tried as you said to send address as 0x4C. It sent 0x98 on SDA line and received the ACK. The DAC is also giving output depending on the First value after control byte. Control byte is 0x10. But the output is not being dependent on the 2nd byte after control byte.

I have written like this

I2caRegs.I2CCNT = 3;

I2caRegs.I2CDXR.all = 0x10;

I2caRegs.I2CDXR.all = I2C_HIGH_D;//0xFF

I2caRegs.I2CDXR.all = I2C_LOW_D;//0xF0

So, when I vary I2C_HIGH_D DAC output is being varied accordingly. But no change in output wrt I2C_LOW_D, Can you I know why is that happening?(1)

BTW as you said i am sending 0x4C instead of 0x98 I dont have control over R/W' in the address byte. It automatically takes Write. Can you tell me how to change to read mode?(2)

0 Manoj Santha Mohan over 6 years ago in reply to Lakshmi Tejas M A

TI__Guru 55700 points

Lakshmi,

Can you please check I2CA_ReadData and I2CA_WriteData function defined in Example_2807xI2C_eeprom.c

Path: <controlSUITE>\device_support\F2807x\v210\F2807x_examples_Cpu1\i2c_eeprom\cpu01

Do you get acknowledgement when 0xF0 is sent?

Regards,
Manoj

0 Lakshmi Tejas M A over 6 years ago in reply to Manoj Santha Mohan

Intellectual 370 points

Hi, Manoj
I am using the same program which u have specified but v180 and yes I am getting ACK after 0xF0 ( 2nd byte after control byte - I2C_LOW_D).

I have updated with the screenshot. it has ack after both 0xFF and 0xF0

Regards,

0 Lakshmi Tejas M A over 6 years ago in reply to Sean Bigley

Intellectual 370 points

Hi Sean,
Can you link to someone who has knowledge about DAC7574?

Regards,
LT

C2000™︎ microcontrollers

C2000 microcontrollers forum

CCS/TMS320F28075: I2c Stop Condition not occurring and first bit missing in data sent