Test points- where it should be in circuit

Thread Starter

ashutosh 123

Joined Feb 26, 2017
37
Hi,

I am working in small project in which the interface flow is
TX-->level translator-->RX

So my doubt is where I need to probe the signal because when signal is transmitting from TX side, the level translator is receiver.So should i need to probe at level translator side or RX side.(for complete measurement of signal rise timd and Fall time etc)
The level translator have both input driver and output driver so when I measure at RX side it is mostly like that signal is transmitting from output driver of level translator.

Can anyone explain me?

Thanks
Ash
 

Thread Starter

ashutosh 123

Joined Feb 26, 2017
37
Hi

I made one ppt for better understanding, Where I need to probe for MOSI (At point 1 and 2)and MISO lines(At point 3 and 4).
If I probe at point 2 for MOSI line then this mosi line is actually driven by Level translator not by TX. If I probe at point 1 then it is actually driven by TX, so I am fully confuse. Can you please help ?

upload_2017-3-26_13-35-20.png
 

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ErnieM

Joined Apr 24, 2011
8,089
Starting at the MOSI line you create a signal at "1" and consume this at "2". What happens at "1" is not important as long as the signal at "2" is correct for the slave.

Same thing for the MISO line, you don't have much care about "4" as long as "3" is good for the master.

This holds true until the day when "2" or "3" is wrong and you want to look at "1" and "4" to troubleshoot.
 

Thread Starter

ashutosh 123

Joined Feb 26, 2017
37
Hi

But what about level translator.it act as input driver for mosi line for receiver.when tx is transmitted the mosi signal actually the level translator is the receiver for that.How can I ignore the input and output driver of level translator.confuse
 

Thread Starter

ashutosh 123

Joined Feb 26, 2017
37
Yes, output of both are same but I have to validate the signal and measure setup time,hold time,rise time ,fall time.
If I measure these parameters at level translator side or receiver side the values will be different.thats y my doubt came
 

ErnieM

Joined Apr 24, 2011
8,089
All those signals are available at points 2 and 3 to measure and validate. You want to characterize the signals at the consumers of same.

Think of it this way: if you wanted to check the reception area of a radio transmitter, would you do this at the radio station antenna, or remotely out in the field somewhere with a radio receiver?

Only if the signals fail will you want to go back to points 1 and 4 to troubleshoot.
 
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