Arno Wagner wrote
Timothy Daniels wrote
Arno Wagner wrote

IDE devices just don't do any termination.
That means that while inactive the IDE device
at the end will just be a very high resistance
digital input. No effect on electical echoes
on the wires at all.

If the input impedance of the device matches that of the
cable, there will be no reflection. That is why high-freq comm
receiver designers try to match the input impedance to the
cable impedance. Are you saying that the input impedance
of ATA devices do not match the impedance of IDE ribbon
cable?

You are entirely correct on how signal termination works.

The input inpedance of an ATA device is a CMOS
input plus ESD protection. Some mega Ohm or more.

Its more complicated than that with most
of the lines that arent pure receivers.

The ATA ribbon cable has an impedance of 200 Ohm,
if I remember correctly. No termination effect at all.

Wrong, the drive presents an impedance
that is different to no drive at all.

For the device in the middle that is how it should be.
Termination in the middle of a signal path is very bad.

Its more complicated than that too if termination is used.

But the end-device has no terminator it turns on.

It has an impedance anyway.

I suspect that at some time that was planned,

Not a shred of evidence of that. ATA has
always been an unterminated system.

but at least the last time I looked at the physical ATA bus
characteristics, there was no mention of it anywhere.

Because it has always been an unterminated system.

That does NOT mean that the drive impedance isnt relevant tho.