I have some questions about AD7995.
Please see the attached file.
Could you give me some adovice?
Thanks in advance.
Tarzan wrote: However You said that just STOP command is fine to reset the register.Please tell me if the wrtting process is nessesary to reset resister.
However You said that just STOP command is fine to reset the register.Please tell me if the wrtting process is nessesary to reset resister.
I reproduced this configuration on my setup and I must admit I was incorrect. The part doesn't return to Channel 0 after NACK+STOP command, it rather continues converting pre-programmed sequence.
According to the above, the writing process to the configuration register is required to restart the sequence.
Apologies for confusion,
Q1. Your assumption is correct. The two channel identifier bits will return the following:
CH1 0 0
CH2 0 1
CH3 1 0
CH4 1 1
Q2. The AD7995 uses internally generated clock for bit trials, therefore an unexpected communication stop is not going to interrupt ongoing conversion. If more than one channel bit has been set in the configuration register, the AD7995 is expected to start conversion on the next channel. This is aligned with what you have seen in your system.
Please be however noted that the part was never designed to cope with this scenario, thus you may see inconsistent behavior, depending on when communication stops.
Thanks for your quick reply.
I understand what you mean.
Please give me a hand if any questions come up.
Hi Jackb S,
I have an additinal question.
AD7995's config resister is set Sequence among V IN0 , V IN1 , V IN2 , and V IN3 mode ([D7:D4]=1111])
But Sometimes our system needs to convert VIN0 After receiving conversion result of VIN2.
Please tell me the procedure in this case.
If we write ([D7:D4]=1111]) again, do you think ADC start conversion from VIN0?
I'm sorry to rush you , but we need to fix the design soon.
I'd appreciated if you give me an answer as soon as possible.
We just want to make sure the way to reset the VIN channel sequence without supply-off
Please refer to my previous post.
Apologies for slow response to your question.
Assuming all channels are selected in the configuration register you are required to issue a STOP condition to interrupt the sequence. This will enable you to read the data from Vin0 on the next read transaction.
There is no need to write to the AD7995 to program a new sequence as STOP conditions doesn't reset the configuration register to its default setting.
Thank for your reply.I really appcieate it.
You mean that issuing STOP command enable to reset vin channel ( setting default condition) ,no matter what?I'm a little bit confused in your previous answer.I have wraped up the question in the slied.Please check it out.
I'm really sorry to ask questions over and over.
Please ask as many questions as you need. We are here to help our customers to find the most appropriate way of operating our products.
Yes, if you issue a STOP command the current sequence is going to be interrupted. If you re-start communication you are expected to read back conversion data from Vin0.
What you have in the PPT presentation is valid I believe.
Thanks for your support.
I really appreciate it.
We just checked how STOP command work as you commented in your previous reply.But the channnel setting did not get clear.Please see the attached file.I thought that no matta what condition s are , STOP condition can reset the register and it become default setting.Please give your opinion abou it.
And I have one more thing to make sure.In our system HOST CPU sometimes stops and starts communicate ADC liked the attached file.But I just wondered if the conversion are done properly.
I summarized these two quesions on the blowing comments of the attached file.
Would you be able to sent NACK instead of ACK before the STOP command is issued? This is raw 14 in your excel file.
I will run similar experiment myself to make sure we get consistent results between the two setups.
With respect to your Q1:
The AD7995 doesn't need an external clock for internal bit trials. It uses an internally generated clock for that purpose. If you stop supplying clock during a middle of conversion of, say channel Vin2, the part will finish this conversion anyway. Please be however noted that the AD7995 was not designed to operate under these conditions hence I would recommend to reconfigure the part as soon as the communication is established. This would help you to ensure that the part is converting on the desired channel.
Thanks for your reply.
This is the typo. I sent NACK before the STOP.Sorry to confuse you.
And one more additional info,
After NACK+STOP, we intentiannaly added the register writing procedure like the fig on the file.It looks that register is reset and channel sequence starts from VIN0.However You said that just STOP command is fine to reset the register.Please tell me if the wrtting process is nessesary to reset resister.
Thank you for the experiments.
I really appriciate your support.
I see what you mean.
If I have futhre questions, please give me a hand.
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