6570 pin is loading loading DUT pin that is generating data

[ChowdaryGBharath]

I'm trying to capture data from device using 6570
When I connect a DUT pin to 6570 DIO2, the output waveform changes and the amplitude decreases

[santo_13]

There are a lot of possible scenarios and the most common one is user error in setting up the pin-state in the pattern. Without more details about the pattern, what DUT is, how it is connected etc., not much guidance can be provided.

[ChowdaryGBharath]

Hi Santhosh,

The pin state is in attached diagram

No pattern is running.

[santo_13]

Please share more details about the DUT and what makes you think that the DUT pin was loaded and what you mean by observe lower amplitude.

Without much information, the problem is definitely one of the following,

1. You've configured the instrument incorrectly
2. Your hardware connections or circuit is incorrect
3. You have misunderstood your DUT or the instrument and hence leading to unrealistic expectations

[ChowdaryGBharath]

Attaching waveforms of signal out from DUT (yellow channel)

Out of the 2 waveforms, one has lower amplitude and looks like doesn't have enough settle time due to high rise/fall times

[santo_13]

Few more questions,

• When you say disconnected - what does it mean? did you disconnect the cable at the connector of 6570?
• What is the drive strength of the DUT and the max bus capacitance it can drive?
• What is the capacitance of the bus (cabling and circuits) until the connector of 6570?

Some more background, some protocols require a limited bus capacitance, for example, the I2C protocol requires the bus capacitance to be <400pF, beyond 400pF the device cannot drive and will potentially not operate properly. Note that any additional PCB trace or coaxial cable adds capacitance to the bus.

I see that the DPI Pin is not loaded because, in your pin state image, you can clearly measure ~3.5V (PPMU pane) which matches with your unloaded scope image. My take is that the DPI by itself did not load the signal but your device may not be able to operate at high speed with the bus capacitance you current have.

Embedding your images for easy reference for others.

Pin State - idle

Pin connected

Pin disconnected

[ChowdaryGBharath]

Hi Santhosh,

Here's my response to queries

• When you say disconnected - what does it mean? did you disconnect the cable at the connector of 6570? - I'm using VHDCI Flying leads cable. I disconnect the DPI pin from berg pin on DUT board
• What is the drive strength of the DUT and the max bus capacitance it can drive? - DUT can drive 25pF at 25MHz. Trace cap on board for the pin is ~15pF
• What is the capacitance of the bus (cabling and circuits) until the connector of 6570? ~15pF