AnalogDiscovery Logic Analyzer Outputting Voltage? (0.9v)

[audiomodder]

Hey all,

First time poster, long time recommender of the excellent AnalogDiscovery and Digilent software :)

  I got the AnalogDiscovery Legacy (black one) and almost blew up an important project today because the logic analyzer was outputting a voltage on it's pins....anyone know why this is / if it is broken?  I measured around 0.9V on DIO 0, 1, etc.

Thanks so much!

P.S. thanks so much for supporting old Windows OS!

[attila]

Hi @EVC

Yes, AD3 DIOs have identical protection + 1M weak pulldown for each line.
AD3 also provides adjustment for DIO drive, slew and pull-up/down/keeper/float.

[attila]

Hi @audiomodder

The DIOs can be used by Logic Analyzer to capture signals, Pattern Generator to output, Static IO and Protocol/UART/SPI/I2C...  for bidirectional use.
The DIOs on AD are output Z/0/3.3V and the input logic threshold is at about 1.5V
If you are measuring 0.9V between DIO and the device GND probably (without driving it from software and external devices/circuits connected) it may be damaged.
You can find the device schematic, DIO protection here: https://digilent.com/reference/test-and-measurement/analog-discovery/reference-manual#digital_io

[EVC]

2 hours ago, attila said:

You can find the device schematic, DIO protection here: https://digilent.com/reference/test-and-measurement/analog-discovery/reference-manual#digital_io

Hi, @attila, is the DIOs of Analog Discovery 3 similar? While troubleshooting the I2C issue I mentioned in other thread, I noticed the low level of SDA and SCL lines, when AD3 is driving them, is around 0.9V with an I2C module whose pull-up resistors are 1kR (5V supplying the I2C module). AD3's RM does not have a diagram of the DIOs, but if those 220R PTCs are present, then that would explain what I observed.

Tks.

[EVC]

19 hours ago, attila said:

Hi @EVC

Yes, AD3 DIOs have identical protection + 1M weak pulldown for each line.
AD3 also provides adjustment for DIO drive, slew and pull-up/down/keeper/float.

@attila, may I suggest the output resistance be added to the specification and/or the RM? Those 220R  may impact some users' projects if they assume the outputs may supply/sink a few mA with VOL/VOH close to 0/3.3V like a regular logic buffer or FPGA GPIO.

FWIW, I love the AD3, is a fantastic little piece of equipment.

BR

[attila]

Hi @EVC

I suggest you check out the Help tab as well. I have tried to add important information, FAQ here.

 

FYI @JColvin

3 hours ago, EVC said:

may I suggest the output resistance be added to the specification and/or the RM? Those 220R  may impact some users' projects if they assume the outputs may supply/sink a few mA with VOL/VOH close to 0/3.3V like a regular logic buffer or FPGA GPIO.

 

[audiomodder]

On 9/11/2024 at 5:00 AM, attila said:

Hi @audiomodder

The DIOs can be used by Logic Analyzer to capture signals, Pattern Generator to output, Static IO and Protocol/UART/SPI/I2C...  for bidirectional use.
The DIOs on AD are output Z/0/3.3V and the input logic threshold is at about 1.5V
If you are measuring 0.9V between DIO and the device GND probably (without driving it from software and external devices/circuits connected) it may be damaged.
You can find the device schematic, DIO protection here: https://digilent.com/reference/test-and-measurement/analog-discovery/reference-manual#digital_io

Thanks for this info and the schems!

It looks like it's still working - whew - even after I stupidly tried to measure a +28v signal :o

The voltage I'm seeing (0.5v now on my meter) appears to be some kind of floating / hi-Z state.  Or possibly some tiny reverse leakage from the high-side diodes.  It appears to go away once I set and arm the GPIO as a logic input and click "run"

Moral of the story: do all of the above steps before connecting sensitive gear.  The FPGA sets the GPIO apparently only after the "run" command is selected in Digilent software (on my black legacy AnalogDiscovery)

Edited September 13 by audiomodder

[attila]

Hi @audiomodder

The DIOs are protected up to +/-20V
I don't know how you use the device, what instruments are you referring to.
When the StaticIO is stopped this does not drive the DIOs. The DIOs can also be driven from Pattern Generator and Protocols. These output the configured initial 0/1/Z value or the protocol specific, on the used/selected DIOs.