Re: [CAD_CAM_EDM_DRO] Re: emc woes

Mcginnis, Darrell S wrote:

>Some cables that pre-date ECP didn't bother to hook up all the status
>and control wires that ECP parallel port modes required (maybe on old
>cables ERRROR or PE are open or maybe SEL was tied lo... in the
>connector housing)
>
>

No, actually there's more to it than that. The IEEE-1284 cable has twisted
pairs inside on the control signals, at least. This greatly reduces
crosstalk
between data lines and the control signals. Plain printer cables just have
a bundle of parallel wires, and the crosstalk is very bad. Old printers had
a lot of delay before accepting data strobes, so they worked with the
crosstalk. The IEEE-1284 was designed to vastly speed up data transfer,
and so everything responds much quicker (about 200 ns, typically) and
is confused by the noise. Even a ribbon cable that absolutely connects
each signal across to the same pin at the opposite end won't work if
it is much more than a foot long.

Jon