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General Hardware Discussion Hard drives, CD, DVD Monitors, All hardware questions not better served by our other Topics


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  #21 (permalink)  
Old 21st March, 2002, 02:32 PM
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Quote:
Originally posted by Wa11y
It would have to connecto to something else to ground it, like a ground lead.
Like pins 2,19,22,24,26,30 and 40? They are all ground!

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  #22 (permalink)  
Old 21st March, 2002, 02:32 PM
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Quote:
Originally posted by Jazz
Well i think one of the pins in the ide port is ground. On both ends it should be grounded. the drive can use either the chassis or the molex power ground.
That would make sense. I found a page with the pinouts for the cable. I'll look for it again.
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Old 21st March, 2002, 02:43 PM
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Quote:
The fact that it is ribbon cable and the fact that the order matters make it very different from the usual telephone cabling, where the multicore is arranged in twisted pair fashion with relatively little attention paid to the ordering.
Twisted pair cables are arranged with current flowing in opposite directions (so the +ve and -ve of each connection would be twisted as a pair). Thus the EM-fields surrounding each wire in the pair oppose and cancel, preventing crosstalk.

My guess is that rounded IDE cables do a similar thing with signal and ground.
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  #24 (permalink)  
Old 21st March, 2002, 05:06 PM
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Quote:
Originally posted by Kaitain
Twisted pair cables are arranged with current flowing in opposite directions (so the +ve and -ve of each connection would be twisted as a pair). Thus the EM-fields surrounding each wire in the pair oppose and cancel, preventing crosstalk.

My guess is that rounded IDE cables do a similar thing with signal and ground.
Actually, if the grounding is done in the connector, it really wouldn't matter if you round it or not, as long as you don't disturb the connection to the connector.
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Old 21st March, 2002, 07:31 PM
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Quote:
Originally posted by Kaitain
Twisted pair cables are arranged with current flowing in opposite directions (so the +ve and -ve of each connection would be twisted as a pair). Thus the EM-fields surrounding each wire in the pair oppose and cancel, preventing crosstalk.

My guess is that rounded IDE cables do a similar thing with signal and ground.
It'd be nice if it did, but it doesn't! As you correctly point out, twisted pair works by having mutually opposing current flows. Any common mode noise (noise of same amplitude on both lines) gets cancelled out when the two signals are subtracted from each other.

Unfortunately, to do this on an IDE cable would require a seperate ground wire from the IDE interface chips on the drive to the IDE interface chips on the mobo, meaning a 66pin connector would be needed. This would allow for the ground return. Alas, the hard disk connector only has 40 pins, so there's no way that the hard disk can set up a dedicated ground return for each signal.

Serial ATA will help in as much as it'll reduce things down to twisted pair communications without the need to sync up so many bits.

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  #26 (permalink)  
Old 22nd March, 2002, 03:57 AM
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This is a very interesting thread, thank you all for creating it! I didn't know why the boost to ATA-66 required a revamp of the IDE ribbon's form factor. Offhand, I thought that larger guage wire meant improved conduction and signal integrity, so making the conductors smaller mystified me. Looks like extremely small voltages(from a greater than CMOS voltage values perspective) "break" this general rule.

After raising the IDE freqs above 33 Mhz, Radio Frequencies now become the major consideration. Doh!

I've read reviews of pre-rounded ATA-100 IDE ribbons that state that brand x works better than stock flat ribbon. No problems with "W" shaped and compressed home rolled ATA-100's, at least in my neighborhood.
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Old 25th March, 2002, 06:27 PM
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ooooh - takes me back

I have'nt seen anything this interesting for quite a while.

Just FYI, the twisted pair cabling thing is known as 'Differential Amplification' and relies on any EMI signal appearing on both conductors, which as previously stated, carry opposing signals, so that the effect is cancelled out at the 'far' end of the cable. There you go, my worthless 2 cents.
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