Re: [CAD_CAM_EDM_DRO line filtering
Posted by
ballendo@y...
on 2000-11-20 22:12:00 UTC
Dave,
Yes, Jon's original post WAS about noise, or at least the poor output
of his p-port. We just went off to the tant. caps question...
<snip> but I believe the real issue was cleaning up noise.
At any rate, to answer your question. First, IBM deleted the 5v
supply line from the original Centronics spec to save pins so they
could use the 25p we now use. And us "real-world interfacing" guys
have paid the price ever since... This means we have to get the power
to do anything beyond simple filtering and impedance matching from
somewhere less convenient. Like the drive connector inside the case.
Or the game port. or the keyboard connector. All of which look like
S@#$.
Jan Axelsons' book "the parallel port" has some good advice re:
impedance matching and filtering. Get it at:
http://www.lvr.com
Second, one of the "unspoken" issues here is the "loosening of the
real world spec" in the p-port interface (meaning that the
manufacturers do not always "put out" or "accept in" what the IBM
spec calls for). Discrete chips have given way to "does it all"
chipsets, which are often the same sort of tradeoff as the 3 in 1
mill/lathe machines we talk about here. So while it may work for a
printer a few feet away, and at a relatively slow pace... For many of
our uses it doesn't. And Jons' usage is prob'ly "pushing the
envelope".
Ballendo
Yes, Jon's original post WAS about noise, or at least the poor output
of his p-port. We just went off to the tant. caps question...
<snip> but I believe the real issue was cleaning up noise.
>I must ask why the filtering doesn't take place adjacent to theIf I'm not mistaken, this is what Jon's boards are.
>parallel connector: i.e. signal condition before you shove the
>outgoing signals down the line to the board set. I'm thinking here
>of a small board that lies between the parallel connector and the
>computer end of the cable.
>Of course this does nothing for the cleaness of the signals going
>the other way.
At any rate, to answer your question. First, IBM deleted the 5v
supply line from the original Centronics spec to save pins so they
could use the 25p we now use. And us "real-world interfacing" guys
have paid the price ever since... This means we have to get the power
to do anything beyond simple filtering and impedance matching from
somewhere less convenient. Like the drive connector inside the case.
Or the game port. or the keyboard connector. All of which look like
S@#$.
Jan Axelsons' book "the parallel port" has some good advice re:
impedance matching and filtering. Get it at:
http://www.lvr.com
Second, one of the "unspoken" issues here is the "loosening of the
real world spec" in the p-port interface (meaning that the
manufacturers do not always "put out" or "accept in" what the IBM
spec calls for). Discrete chips have given way to "does it all"
chipsets, which are often the same sort of tradeoff as the 3 in 1
mill/lathe machines we talk about here. So while it may work for a
printer a few feet away, and at a relatively slow pace... For many of
our uses it doesn't. And Jons' usage is prob'ly "pushing the
envelope".
>Maybe someone can review the pro's and con's of this one.Hope this helps.
>Tnx. Dave
Ballendo