GX 5295 External Clock Input
Pramod K.
Bangalore, Karnataka

Oct 9, 2012
3 Posts

GX 5295 External Clock input

Hi all,

     Has anyone used GX 5295 digital I/O  in the external clock input mode? Whether the digital I/O behaves the same as it was when using the internal clock? Any steps should be taken for setting up the digital I/O to make it use the external clock?

Will be expecting a solution as soon as possible.

Thanks & regards
Pramod Kumar

Dale J.
La Verne, CA

Oct 9, 2012
10 Posts

Re: GX 5295 External Clock input

Hello Pramod,
The GX5295 IO functions the same on external clock as it does on internal clock, with the following exceptions.

1.  When arming the DIO, the clock source is used to clock the internal state machine to set it up for running.  If you are on external clock, and the clock is inactive, the arming function will time out.

2.  Programmable delay of the clock and strobe is a function derived from the internal PLL's when using internal clock.  With an external clock, the PLL's are out of the circuit, so programmable clock and strobe delays do not function.  The same is true for channel deskew.

Regards,
Dale Johnson

Pramod K.
Bangalore, Karnataka

Dec 20, 2012
3 Posts

Re: GX 5295 External Clock input

Hi Dale Johnson,

We tried the following using GX5295 DIO to check whether the external clock is working.

1. We applied 1MHz clock from the DIOEasy, we were able to see the same 1MHz output in the Oscilloscope from the Clock Out(Pin number 22) when the clock source is internal. Now for external clock, we are giving input from the functional generator. We applied the 1MHz clock from the functional generator and checked in the oscilloscope for verification. It was working fine. But when I bring this connection near the external clock input pin of the DIO, that is pin number 31 of the DIO my input was pulled down to ground level. So we checked the connector for any shorts. But the connector looks fine. So I want to know what may be the reason for this? Or is there any jumper on the board that we have to enable when we are using external clock?

2. There is an external clock enable pin(pin number 28) which mentioned as active low enable. If  I want to make it to active high what is the maximum voltage that I can apply to that pin?

Best Regards,
Pramod Kumar

Dale J.
La Verne, CA

Dec 20, 2012
10 Posts

Re: GX 5295 External Clock input

Hello Pramod,
I verified operation of external clock on a GX5295 here.  Possible reasons why external clock is not working in your configuration:
1.  External Clock levels are wrong.  What are the levels and offsets of your external clock?  Sine or square wave?  The external clock input is LVTTL compatible.  My signal was 0V - 3.5V.
2.  Source has weak drive.  What are you using to source the external clock input?  The GX5295 external clock input is terminated 100 ohms to V+ and 100 ohms to GND (50 ohm equivalent).  Can your source drive this load?
3.  Wrong connector or pin.  Since you are measuring the output clock on pin 22, I assume you are on the J3 connector connected to pin 31 for the external clock input.  But you may want to verify that you are on pin 31.
4.  Possible defective hardware.  What is the serial number and firmware revision of the GX5295?  You can find this in the "About" tab of the GtDio Soft Panel.  Can you connect your source to the external strobe input to see if you have similar attenuation?  It has the same 100 ohm to Gnd/V+ as the external clock.

The external clock enable signal is a hardware input for selecting the external clock as your clock source.  You can also select the external clock using the DioEasy Panel, or with an API function.  I used the software command and the external clock enable to select the external clock.  Both worked as expected.

Please let me know what you find.

Regards,
Dale

Pramod K.
Bangalore, Karnataka

Jan 21, 2013
3 Posts

Re: GX 5295 External Clock input

Thanks Dale,

We found out the issue and it was the Source which had a weak drive. The External clock input pin actually requires 32mA current for its operation. Our source was not capable of that. So we placed a digital buffer in between the source and the DIO and finally we were able to make the External clock of the DIO work.  No more issues regarding that. Thanks for the help.

Regards,
Pramod


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