DAC8760: Interfacing Dac8740h with Dac8760 for Hart communication using ISET-R PIn

Lucas is reviewing this now.

Hi Ankush,

What does your HART sinusoid look like when you are attempting 0 - 24 mA? Please plot the input and output across a load.

Thanks,
Lucas

Here are the waveforms,

This is the hart signal  transmitted from from Hart communicator.

Slave device does not show  any response hart signal transmitted to communicator (zoomed out image below)

Hart communicator TX signal pulses

signal at mod in pin of dac8740h

signal at mod out pin of dac8740h

Hi Ankush,

To verify, can you plot the status of the CD (carrier detect) pin during those TX signal pulses?

The UART_OUT of the DAC 8740H should also be sending the HART bits, which can be used to doublecheck the DAC8740H is outputting correctly.

Can you also check the DC point of reference for your oscilloscope or run the plots in DC mode to ensure it is centered around 0 V?

Thank you,
Lucas

Hi lucas,

Sorry for the late reply.

Here are the waveforms you requested.

Hart Communicator TX waveform and waveform at CD PIN.

 Waveform at MOD IN PIN and waveform at CD PIN.

Waveform at MOD OUT PIN and waveform at CD Pin

Thank you,

Ankush

We will respond on Monday, after the US holiday.

Hi Ankush,

Let me doublecheck your plots with another engineer and I will get back to you tomorrow.

Thanks,
Lucas

Hi Ankush,

Were you able to plot your HART signal in DC mode to ensure it was centered around 0 V?

Thanks,
Lucas

Hi Lucas,

Here are the waveforms captured in DC coupling mode.

Waveform at MOD IN pin and CD pin

Waveform at Mod  IN pin and CD pin  (zoomed in)

Waveform at Mod  OUT pin and CD pin

Waveform at MOD OUT PIN (zoomed in)

Waveform at Mod  IN pin and CD pin

Hi Ankush,

Is your UART_OUT pin on the DAC8740H matching up with your HART signal?

Your above signals look like it is working, can you clarify what you meant in your original message by "unable to establish a successful communication"?

Thanks,
Lucas

Hi Lucas,

On the same software code my slave device communicates with the hart communicator and vice versa when I use Hart IN pin configuration.

For HART IN method I use  C36 and C29 : 10nF/50v  Capacitor and I enable 4-20mA mode,HART IN pin of DAC8760 through software. So I don't think there is any issue from UART side. 

For ISET-R method  I have assembled components  mentioned in this document  "Application Report SLAA572 – January 2014" 

Slave device receives data from communicator but communicator doesn't receive data from slave.

The Wave forms I sent in my previous posts are  between DAC8760 and DAC8740. I'm not detecting TX waveform from slave device on 4-20 mA output PIN

Do I have to change something from software side for ISET-R?

Hi Ankush,

I agree that this part of the datasheet is missing some important context.

RSET's tolerance is directly proportional to the gain error of the output, so 1% accuracy would be 1% error. I recommend using the most accurate resistor available.

Thanks,
Lucas