6602 / hardware / filtering

[ztruth]

Hi All

System Specs:

I am using a 6602 pci card (R6868 cable to TBX68).

I have LV8.2 code to output (4) 1KHz counter outputs (3) of which are delayed by 1us.

I use Same Trigger for all (4) continuous counters from io port0 line0 to PFI38.

Issues:

The 5V TTL high level of the 1st counter exhibits a 1V dip during the rise time of the other 3 delayed counters.

Support requested:

1. How to; filter the voltage dipping affect ?

2. How to; decrease the rise time [currently100ns].

Thanks

Ryan

[AnalogKid2DigitalMan]

1. What is the device and it's input characteristics that the counter signals are connected to? Wondering if it is excessively loading down the counter outputs? May need a buffer or line driver chip between the 6602 and your device.

2. Risetimes can be slowed down with resistor/capacitor filtering.

[ztruth]

First I measured unconnected cnt0 output; and then connected and measured LM 6125 buffer out; both methods gave exact same dip and rise time mesasurements. 

[ztruth]

To recap

I am not driving the device yet

I am not using any resistors or caps at this point

With and without buffering, I measure dip of 1v and rise time 100ns.

I tried two different 6602 computer systems and both exhibit these same characteristics.

How might I reconfigure and/or filter 6602 output to improve "counter cross talk" dip; and risetime?

Thanks

Ryan

[AnalogKid2DigitalMan]

Hi ztruth:

If the counter output droops without the 6125 connected, then I am guessing maybe the other 3 counters are dragging it down (poor board design or excessive loading- I do not know) but even with 1 volt droop it still conforms to TTL logic level high specifications. What are the other 3 counters connected to? Have you repeated the test with them disconnected also?

I misread your request on risetime- you can't decrease from within the board, maybe a high speed schmitt trigger would help prior to the 6125's input.

According to what I saw on the Web, the LM6125 has been out of production for nearly 12 years. It is a nice chip though. What are you driving with it?

-AK2DM