IDE Ribbons - open ended?

[Choozo]

Hi all,

Is there any reason for NOT leaving one end open on a 80-conductor ATA/66 IDE ribbon?
I have wired my two IBM DTLAs as master on each channel, and used the 'middle' ribbon connector to the HDs since this let me have the shortest way between the IDE port and the HD.

In a Operation Manual for a Plextor Writer I found the following Caution on IDE connectors:

"<b>CAUTION:</b> In the case of only one IDE device, you must make certain that one end of the cable is always connected to the IDE connector on the motherboard. The other end of the connector must be connected to a device. The end connector of the cable should never be left unconnected."

I guess this can be interpreted two ways - 'middle-end' or 'end-end'? http://www.linuxnewbie.org/ubb/smile.gif .... Anybody here that have any thoughts on this?

[mdwatts]

end-end as how I interpret the quote.

I've read similar instructions in a Compaq manual for my new work PC.

[MGP]

Here's the deal on 40 pin/80 conductor ATA66 cables:

The "extra" 40 conductors are placed one each between the "normal" 40 IDE signal conductors. They are attached to DC ground on the motherboard side of the connector and form a shield between each of the active IDE signals. This produces much less crosstalk (one IDE signal inducing noise on the one next to it) and reduces the amount of EMI noise on the IDE signal from the high frequencies inside the computer chassis.

There is a correct polarity to ATA66 cables -- most cables have a different colored connector (blue, usually) that goes to the motherboard IDE connector. It MUST be attached to the motherboard correctly for the shielding to work, otherwise the "shields" become an antenna for noise and can actually make the signal/noise ratio on the IDE signals worse. It's possible you will get random IDE errors or the drive won't work at all if the cable is not connected with the correct polarity.

You should also connect a single drive to the END connector for the same reason. A 6" cable stub hanging off your IDE drive acts like an antenna for noise also, since the signals and shield are unterminated (have no electrical load) for the last 6".

Hope that helps!

[Choozo]

Great, thanks!

I opened the box again and reconnected the IDE devices to the END of each ribbon. Sounds reasonable that the ribbon should be 'terminated' anyway, although this is not entirely like a SCSI system.