Re: gEDA-user: basic anti-EMI design q

[Bill Sloman <bill.sloman@xxxxxxxxx>]

At 05:21 24-3-2006, you wrote:
> DJ Delorie wrote:
>
> > It's not the drivers that mess up, it's the octal latch.
>
>
> if the existing latch is in the interface with ribbon cable to the 
> PC  - there's your problem.

Have you grounded every second wire in the ribbon cable? It sounds 
extravagant, but if you need shielding, that's a commonly used way of 
getting it. It also means that the residual signal wires look like 
50R transmission lines. You can get shielded ribbon cable, but it is 
expensive, and grounding the shielding isn't always that easy - you 
need metal (or metallised) connector shells, and they aren't always 
easily available.

> You could probably fix it with something gross like series R in the 
> line and a bypass cap to ground (the ground the latch sees - the 
> chips pin 10) right at the octal latch.

Some logic specifies minimum edge speeds on clock inputs. Too much 
filtering can make the logic do funny things.

<snip>

Bill Sloman, Nijmegen