Re: gEDA-user: terminators

[gene glick <carzrgr8@xxxxxxxxxxxxx>]

DJ Delorie wrote:
>> Are you willing to put some buffers at the end of your bus?
> 
> Like a pair of 74AVC16244's ?  They'd have to be mounted on the back
> of the board, under the bus where the stubs go.
> 
> 
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Yeah that looks ok.  It's got a 6 pF input capacitance.  For a 1-nS 
edge, I figure 6 pF is going to have around 27-Ohm reactance.  So you'll 
have a little mismatch to your trace, maybe a little ringing.  Beats 
loading it with an inductive stub.

I think this is an ok method as long as you realize there will be some 
timing distortion in your measurements. At 133 MHz, the cycle time is 
7.5 nS.  Hopefully, the internal skew inside the buffer is fairly 
constant (within a single package, it'll be pretty tight), and the 
flight time on your cable is matched.

What voltage are you running?  I see the tpd gets slow as the supply is 
lowered.


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