Can IDE cable's end connector be left idle ( w-o affecting data transfer ) ?

[TE Cheah]

Per www.pcguide.com/ref/hdd/if/ide/confCable-c.html
"Using the middle connector and leaving the end connector unattached
...... leaves part of the cable "dangling". This is called a stub and creates
much worse electrical characteristics on the cable, due to reflections
from the unterminated ends of the cable wires. It is not recommended."

I 1st ignored this warning, & found my Toshiba cd drive ( using cable
select, & assigned by Award bios as 2nd channel's slave device )
though can play any VCD just as well, cannot pass BCM diagnostic (
blue screen of "fatal error" appears in Win98se ) unless I use the end
connector of this 80 wire cable to connect this drive ( i.e. bios
assigned as master device ) to my ( VIA ) kt266a 's hdd controller.

Does any1 here have a similar experience ? If this warning is valid,
then why does no mboard / hdd / cdd / dvd / cable manufacturer warn
users of this requirement ?

 

[Arno Wagner]

Per www.pcguide.com/ref/hdd/if/ide/confCable-c.html
"Using the middle connector and leaving the end connector unattached
..... leaves part of the cable "dangling". This is called a stub and creates
much worse electrical characteristics on the cable, due to reflections
from the unterminated ends of the cable wires. It is not recommended."

I 1st ignored this warning, & found my Toshiba cd drive ( using cable
select, & assigned by Award bios as 2nd channel's slave device )
though can play any VCD just as well, cannot pass BCM diagnostic (
blue screen of "fatal error" appears in Win98se ) unless I use the end
connector of this 80 wire cable to connect this drive ( i.e. bios
assigned as master device ) to my ( VIA ) kt266a 's hdd controller.

Does any1 here have a similar experience ? If this warning is valid,
then why does no mboard / hdd / cdd / dvd / cable manufacturer warn
users of this requirement ?

First, IDE cables are not terminated. That means that for the drive on
the middle connector it makes no difference whether there is a drive
at the end or not! If anybody says different, then they do not
understand the subject matter. In SCSI cables (what likley causes
the confusion) it is a different matter: The last device on an
SCSI bus _is_ terminated and havinf no device there either means the
bus is not terminated or it is teminated somewhere in the middle.
Both useually cause mor or less secvere problems. Again, the same is
_not_ true for IDE cables. The device at the end does _nothing_ for
signal quality when the controller and the device in the middle
talk to each other. From the point of view of the device in the
middle, the end-connector is allways empty. The only exception is
during the power-on sequence, but not during normal operation.

That said, yes, the electical characteristics are worse, but any
well-designed IDE device needs to be able to deal with it. I do have a
TEAC CD-writer (CD-W540E) that is sensitive to rounded cables when
data is transferred to the device. I get bit-errors on the written
CDs. The burner has no problems with normal flat cables, no matter
what connector it is on. I would say the device is borderline broken
by design. If you use standard length flat cables then the CD drive
or IDE controller has likely been damaged, e.g. by static electricity.
It usually makes digital I/Os much more sensitive to noise.

Arno

 

[glee]

You are correct as far as what that particular web page refers to: 40-pin,
80-wire IDE cables.

It is my understanding however (and the recommendation of the
manufacturers), that 40-pin, 80-wire IDE cables *do* require particular
devices to be attached to particular connectors on those cables, and that
the end connector *not* be left vacant. This is especially true in the
example given in the original post: using Cable Select.

http://www.pcguide.com/ref/hdd/if/ide/conf_Cable80.htm

 

[BobT]

Does any1 here have a similar experience ? If this warning is valid,
then why does no mboard / hdd / cdd / dvd / cable manufacturer warn
users of this requirement ?

Not a "requirement" but recommended. And they do, check out Maxtor's
installation instructions, for example.

 

[Peter]

Per www.pcguide.com/ref/hdd/if/ide/confCable-c.html

First, IDE cables are not terminated. That means that for the drive on
the middle connector it makes no difference whether there is a drive
at the end or not! If anybody says different, then they do not
understand the subject matter.

Thats your personal opinion.
Standard documents disagree with you:
"T13/1410D revision 3b
Page 11
The host shall be placed at one end of the cable. It is recommended that for
a single device configuration the
device be placed at the opposite end of the cable from the host. If a single
device configuration is implemented
with the device not at the end of the cable, a cable stub results that may
cause degradation of signals. Single
device configurations with the device not at the end of the cable shall not
be used with Ultra DMA modes."

In SCSI cables (what likley causes
the confusion) it is a different matter: The last device on an
SCSI bus _is_ terminated and havinf no device there either means the
bus is not terminated or it is teminated somewhere in the middle.
Both useually cause mor or less secvere problems. Again, the same is
_not_ true for IDE cables. The device at the end does _nothing_ for
signal quality when the controller and the device in the middle
talk to each other.

That is wrong understanding.

From the point of view of the device in the
middle, the end-connector is allways empty. The only exception is
during the power-on sequence, but not during normal operation.

That said, yes, the electical characteristics are worse, but any
well-designed IDE device needs to be able to deal with it.

But it might affect performance (retries) and create less stable
communication environment. If other environmental conditions change (power,
temperature, EMI), your device might not be able to communitate at all.

I do have a
TEAC CD-writer (CD-W540E) that is sensitive to rounded cables when
data is transferred to the device. I get bit-errors on the written
CDs. The burner has no problems with normal flat cables, no matter
what connector it is on. I would say the device is borderline broken
by design.

I would rather say that rounded cables are out of IDE spec.

 

[Folkert Rienstra]

Not a "requirement" but recommended.

It's a requirement if you want to use the higher Ultra-DMA modes.

 

[Folkert Rienstra]

First, IDE cables are not terminated.

Neither are SCSI.

That means that for the drive on the middle connector it makes no difference
whether there is a drive at the end or not!

Yes it does. Even more so, in fact.

If anybody says different, then they do not understand the subject matter.

Practicing before that mirror again, babblemouth?

It's you who obviously doesn't understand.

In SCSI cables (what likley causes the confusion) it is a different matter:

No. it's not. Just a different solution to a problem.
Terminators come seperate from drives.

The last device on an SCSI bus _is_ terminated and havinf no device there
either means the bus is not terminated or it is teminated somewhere in the middle.

Utter nonsense, clueless as always.
Drive internal terminators were last seen on
Ultra SCSI devices and only on few of those.

Both useually cause mor or less secvere problems.

Have you been boozing again, babblemouth?

Again, the same is _not_ true for IDE cables.

Corse it is.

The device at the end does _nothing_ for signal quality when
the controller and the device in the middle talk to each other.

Corse it does. And it's not different to SCSI either.

From the point of view of the device in the
middle, the end-connector is allways empty.

Gee, where is the difference with SCSI there.

The only exception is during the power-on sequence,
Nonsense.

but not during normal operation.

That said, yes, the electical characteristics are worse, but any
well-designed IDE device needs to be able to deal with it.

And with Ultra DMA they do by introducing series termination.
It's on the drives that can do Ultra-DMA.

[Stupid off-topic rant snipped]

 

[glee]

You are correct as far as what that particular web page refers to: 40-pin,
80-wire IDE cables.

Correction/Typo: That should read: 40-pin, 40-wire IDE cables. Brain
failure (again)!

I'm not sure I should go so far as to say you are correct there, either.....
there can and will be the possibility of "electrical disturbances"
regardless.

....glen

 

[Timothy Daniels]

"Using the middle connector and leaving the end connector unattached
..... leaves part of the cable "dangling". This is called a stub and creates
much worse electrical characteristics on the cable, due to reflections
from the unterminated ends of the cable wires. It is not recommended."

This is true - that it's not recommended - and for the reason given.
An open circuit at the end and a short circuit at the end of a cable
are equally reflective of signals. And that is why the cable length and
the connector spacing is specified for IDE cables - to minimize the
effects of signal reflections that do occur. BUT... some circuit designs
are more tolerant of signal reflections than others, and *sometimes*
you can get away with the end connector empty. In my PC with a SIIG
PCI IDE controller and Maxtor DiamondMax Plus 9 hard drives, an
empty end connector seems not to matter - bootups and disk cloning
seem to take the same amount of time when the destination disk is on
the middle connectore or on the end connector of channel 1. But I
wouldn't count on that being the case for all hard drives and for all
IDE controllers, and I don't even do that in my PC in normal procedure.

If your question derives from a desire to keep down the amount
of ribbon cable in the PC's interior, try "round" cables. They come in
various lengths in both single connector and dual connector forms,
and some models have aluminum or copper braid shielding.
They do "flout the ATA specs" as one poster would complain, but
I've had no problems with them, and they do clean up some
"impossibly crowded" case interiors. Check 'em out:
http://svc.com/cables-ata-100-133-round-cables.html

*TimDaniels*

 

[Arno Wagner]

You are correct as far as what that particular web page refers to: 40-pin,
80-wire IDE cables.

Same for 40 pin 40 wire cables.

It is my understanding however (and the recommendation of the
manufacturers), that 40-pin, 80-wire IDE cables *do* require particular
devices to be attached to particular connectors on those cables, and that
the end connector *not* be left vacant. This is especially true in the
example given in the original post: using Cable Select.

In fact cable select is the only reason for this. There is no other
one. If you jumper the devices to slave/master you can have them in
arbitrary order, number and position on these cables.

With cable select the device at the end is the master (during
boot-up) and the device in the middle the slave. Some devices will
fail to start or have problems if they are used as slave and no master
is present. AFAIK this is more of a historic problem today.

Arno

 

[Arno Wagner]

Correction/Typo: That should read: 40-pin, 40-wire IDE cables. Brain
failure (again)!

I'm not sure I should go so far as to say you are correct there, either.....
there can and will be the possibility of "electrical disturbances"
regardless.

True. There will be signal echoes on the wires. The enpoint
will indeed get a significantly cleaner signal.

But as I said a device at the end will not improve the
situation for the device in the middle in any way. It does not
matter whether it is an 40/40 or an 40/80 cable. 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 you have a borderline broken device, then you may observe it
only working on the cable end. However if you have a correctly
working device it must work in both positions, regardless of
whether another device is present. (Disregarding the CS/jumpers
issue for the moment.)

Arno

 

[Arno Wagner]

Thats your personal opinion.

No, that is electrical engineering. Read any text on digital signal
transmission of copper wires. And T13 does specify the inputs
in a way that no termination at all is going on.

Standard documents disagree with you:

[... disagreeng part snipped ...]
Which does not make sense from an EE point of view. Maybe they
wrote this when they actually intended to add termination to the
electonics. With 80 pin wired a device can tell it is at the end
and could then turn on an active terminator. But AFAIK there
is no such design requirement or possibility in the standard.

Arno

 

[Eric Gisin]

Idiot Troll Alert!!! Arnie is well known for posting bullshit.

All ATA devices have internal termination.

 

[Peter]

First, IDE cables are not terminated. That means that for the drive on

No, that is electrical engineering. Read any text on digital signal
transmission of copper wires. And T13 does specify the inputs
in a way that no termination at all is going on.

When did you study electrical engineering (if at all)?

For those frequencies, attached piece of cable does not behave like nothing.
And YES, there is a termination as described by T13:
"4.2.2.2 Series termination required for Ultra DMA"
Otherwise, signal reflections will cause increased and substantial
interference.

Standard documents disagree with you:

[... disagreeng part snipped ...]

You can snip whatever you like, T13 document is still there:
http://www.t13.org/docs2002/d1410r3b.pdf

Which does not make sense from an EE point of view. Maybe they
wrote this when they actually intended to add termination to the
electonics. With 80 pin wired a device can tell it is at the end
and could then turn on an active terminator. But AFAIK there
is no such design requirement or possibility in the standard.

Or maybe T13 guys did not study electrical engineering at the same place as
you did.

 

[Oscar]

True. There will be signal echoes on the wires. The enpoint
will indeed get a significantly cleaner signal.

But as I said a device at the end will not improve
the situation for the device in the middle in any way.

Wrong, it reduces the 'signal echoes' which are actually
the sharp edges getting reflected off the impedance
discontinuity. Thats reduced with a drive on the end.

It does not matter whether it is an 40/40 or an 40/80 cable.
IDE devices just don't do any termination.

Irrelevant. The drive has a different impedance to no drive.

That means that while inactive the IDE device at the
end will just be a very high resistance digital input.

Wrong again.

No effect on electical echoes on the wires at all.

Wrong again. Its significantly different impedance to no drive.

If you have a borderline broken device, then you may observe it
only working on the cable end. However if you have a correctly
working device it must work in both positions, regardless of
whether another device is present. (Disregarding the CS/jumpers
issue for the moment.)

Separate issue entirely.

 

[Oscar]

Same for 40 pin 40 wire cables.


In fact cable select is the only reason for this. There is no other
one. If you jumper the devices to slave/master you can have them in
arbitrary order, number and position on these cables.

Pity about what the ata standard recommends.

 

[Oscar]

No, that is electrical engineering.
Nope.

Read any text on digital signal transmission of copper wires.

None of which say that no drive has the same impedance as a drive.

And T13 does specify the inputs in a
way that no termination at all is going on.

Termination is an entirely separate issue to whether no drive
has a different impedance to a drive on the end connector.

THATS why the standard recommends that a single drive be on the end
connector.

Standard documents disagree with you:

[... disagreeng part snipped ...]

Which does not make sense from an EE point of view.
Wrong.

Maybe they wrote this when they actually
intended to add termination to the electonics.

Or maybe they realise that a drive on the end connector
is electrically different impedance wise to no drive there,
even if you dont.

With 80 pin wired a device can tell it is at the end and
could then turn on an active terminator. But AFAIK there
is no such design requirement or possibility in the standard.

Yep, you're off on a red herring there.

 

[Timothy Daniels]

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?

*TimDaniels*

 

[Timothy Daniels]

In fact cable select is the only reason for this. There is no other
one. If you jumper the devices to slave/master you can have them in
arbitrary order, number and position on these cables.

You are correct that *on a single IDE channel*, the device arrangement
can be Master/Slave or Slave/Master or single Master or single Slave.
What is not allowed by the IDE controller, though, is Master/Master and
Slave/Slave on the same channel. But on different channels, you could
have ch.0 Master/ ch. 1 Master and ch. 0 Slave/ ch. 1 Slave and
ch. 0 Slave/Master/ch. 1 Master/Slave. The arrangement prohibited is
having the same jumpering for both devices on the same IDE channel,
i.e. on the same cable. That is imposed by the controller's need to be
able to tell the two devices apart which are on the same cable. I think
that's what you intended to express, but it wasn't clear.

And the implications go farther: A Slave HD can be the "boot drive"
just as well as well as a Master HD. All that is required is that the HD
be at the head of the HD boot order. The default settings (or settings in
BIOSes which don't enable adjustment of the HD boot order) put the
Master on ch. 0 at the head of the HD boot order. But this can be
changed by readjustment of the HD boot order. Indeed, it's quite
legitimate to have the Slave on ch. 1 (the secondary IDE channel) be
the "boot drive".

*TimDaniels*

 

[Rod Speed]

Arno Wagner wrote

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?

Yep, if that was the system, it would be specified in the standard.