CCS/DAC7574: Not dependent on Lower byte, TMS320F28075, I2C

Lakshmi Tejas M A

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

Tool/software: Code Composer Studio

HI,

I am using TMS320F28075 with DAC7574. The DAC7574 is giving output depending on the First value after control byte(high byte). Control byte is 0x10. But the output is not being dependent on the 2nd byte after control byte(lower 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 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)

over 6 years ago

0 Uttam Sahu over 6 years ago

TI__Genius 14220 points

Hi Lakshmi,

Thank you for your query. I am looking into it. Will get back to you soon.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs

0 Uttam Sahu over 6 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Lakshmi,

Sorry for the late reply. Could you please send me a scope capture of the I2C waveforms? If you feel that the waveforms are not according to your code, you can post a query on the MSP430 forum - they will be in a better position to answer.

Regards,
Uttam

0 Lakshmi Tejas M A over 6 years ago in reply to Uttam Sahu

Intellectual 370 points

HI Uttam,
Thanks for looking through the thread. You can see the screenshot here : e2e.ti.com/.../4555.TEK00002.PNG

I actually raised the thread in c2000 form and waveforms are correct:
e2e.ti.com/.../594060

Regards,
Lakshmi

0 Uttam Sahu over 6 years ago in reply to Lakshmi Tejas M A

TI__Genius 14220 points

Hi Lakshmi,

Very sorry for keeping this pending for so long. I somehow missed this thread.

The I2C waveform looks fine to me. Do you think there is a problem in probing the output etc? Are you testing it on an EVM or your own hardware? Is it possible for you to share your schematics, if it is your own hardware?

Please change the channel and the data and try to see if there is any impact.

Regards,
Uttam

0 Lakshmi Tejas M A over 6 years ago in reply to Uttam Sahu

Intellectual 370 points

Hi Uttam,
Thanks for the reply. I am working on the EVM. I don't think its a problem with probing because I am probing at DAC output jumper only. Output is varying wrt I2C_HIGH_D only.

Regards
Lakshmi

0 Uttam Sahu over 6 years ago in reply to Lakshmi Tejas M A

TI__Genius 14220 points

Hi Lakshmi,

Is it possible for you to share your schematics? If it is confidential, send me a friend request on the forum and then I will share my email-id as a private message. You can then share the files over email.

By the way what multimeter are you using? You may not be able to see the LSB variations if the multimeter is not accurate enough. The maximum voltage by the 4 LSBs will be around 20 mV, which may not be detectable unless you use a proper multimeter.

Regards,
Uttam

0 Lakshmi Tejas M A over 6 years ago in reply to Uttam Sahu

Intellectual 370 points

Hi Uttam,
I am using the schematics given bye DAC7574EVM.
www.ti.com/.../slau117a.pdf

I am using a SCOPE: Tektronix DPO2024. It can measure variations in mV.

Regards
Lakshmi

0 Uttam Sahu over 6 years ago in reply to Lakshmi Tejas M A

TI__Genius 14220 points

Hi Lakshmi,

I would suggest you to use a multimeter. Usually the scope noise might mask the signals in mV.

Even a standard 3-1/2 digit lab multimeter should be fine.

Regards,
Uttam

0 Lakshmi Tejas M A over 6 years ago in reply to Uttam Sahu

Intellectual 370 points

Hi Uttam,
I am using fluke 179 multi-meter, i see change with lsb. it works thanks a lot. Measured with higher decimal bit multi-meter I can see full proper resolution
Regards
Lakshmi

Data converters

Data converters forum

CCS/DAC7574: Not dependent on Lower byte, TMS320F28075, I2C