DS90UB914Q-Q1: No signal at PCLK when giving commend first

Cindy Chang

Part Number: DS90UB914Q-Q1

Hi ,

We're using DS90UB913 and 914 to transmit and receive data with 20m cable connected in between.

When we give the commend, 0x60 0x3f 0x00, and then put probe of oscilloscope (CH4) on PCLK pin, there's no PCLK signal. [pic 1]

However, if we put probe of oscilloscope (CH4) on PCLK pin first and then give the commend, 0x60 0x3f 0x00, there's signal coming up at PCLK. [pic 2]

Why there's a different between these two measuring method?

Thank you.

[pic 1] [pic 2]

Best,

Cindy

over 5 years ago

0 Hamzeh Jaradat over 5 years ago

TI__Guru** 107910 points

Hello Cindy,

are you measuring 12MHz PCLK?

Can you please clarify what is Pink color and what is orange ?

0 Cindy Chang over 5 years ago in reply to Hamzeh Jaradat

TI__Intellectual 2475 points

Hi Hamzeh,

Pink and orange are just like what be marked in schematic: CH4 and CH1.

Thank you.

Best Regards,

Cindy

0 Hamzeh Jaradat over 5 years ago in reply to Cindy Chang

TI__Guru** 107910 points

Hello Cindy,

Thanks. With this your discription is not clear!!

You are saying once you apply that command, you can't measure PCLK, but the I can see PCLK (Pink) is always present!!

Also this PCLK value is not valid. You are measuring only 12MHz which is not supported by this pair of devices!!

0 Cindy Chang over 5 years ago in reply to Hamzeh Jaradat

TI__Intellectual 2475 points

Hi Hamazeh,

Oh... it's my mistake.

We could not measure CMLOUT signal if we give commend first.

I think this might because impedance change.

If we probe first, the impedance will be smaller due to paralleling cable and probe.

Is this correct?

And why 12MHz PCLK value is not valid?

Thank you.

Best Regards,

Cindy

0 Hamzeh Jaradat over 5 years ago in reply to Cindy Chang

TI__Guru** 107910 points

Hello Cindy,

to measure CMLOUT you do need AC-Coupling capacitors (100nF) as shown below.

Okay you are using the 914Q not the 914A. So 12MHz PCLK is supported on the 914Q.

0 Cindy Chang over 5 years ago in reply to Hamzeh Jaradat

TI__Intellectual 2475 points

Hi Hamzeh,

I could not see your picture...

Thank you.

Best Regards,

Cindy

0 Hamzeh Jaradat over 5 years ago in reply to Cindy Chang

TI__Guru** 107910 points

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DS90UB914Q-Q1: No signal at PCLK when giving commend first