Q&A Issue with recognizing the start bit in the preamble of AD5700

Issue with recognizing the start bit in the preamble of AD5700

DKhrip

on Jan 15, 2025

Category: Hardware

Product Number: AD5700

Hello!

I am using the AD5700 chip for implementing a HART interface. The issue is that the chip fails to recognize the start bit in the preamble.

Tell me, what could be the problem? Thank you!

Tags: hardware HART Interface Solutions ad5700 ad5700 ad5700-1 hart 4-20ma Start Bit hart hart_modem Show More

0 DKhrip
on Jan 15, 2025 3:57 AM
Here are oscillograms at different points in the circuit
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0 dendalisay

on Jan 17, 2025 2:09 AM in reply to DKhrip
Hi DKhrip ,

isantos will be queuing this query and will get back to you soon.

Br,

Den
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0 isantos

on Feb 25, 2025 6:05 AM in reply to DKhrip
Hi DKhrip ,

Apologies for the delay, do you still need help with this query?

Things you could try to do:

1) monitor the CD pin to make sure that carrier detect works well at the start of your preamble (similar to Figure 5 of the data sheet)

2) use the part in DUPLEX mode just to test a different HART source

Looking at the HART signal though, they don't look like close to sine wave. The waveshape affects how the demodulator detects and demodulate the signal as it goes through series of filters within the device.

Could you review of the waveshape is within specifications of HART physical layer?
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