ATA anomaly Question

[Bill Hacker]

Joerg Sonnenberger wrote:

On Sun, Mar 20, 2005 at 03:31:28AM +0800, Bill Hacker wrote:

  Typically the cable is reversed (motherboard side is connected to the
  drive and the drive side is connected to the motherboard) when the
  message occurs for a standard PATA drive and the cable is 
  UDMA-capable.
Most sockets & headets are keyed (blocked pin position) to prevent
that (at least on the better cables I try to use). Ground leads 'float'
at one end, are collected at the other end, IIRC.


The problem is that you can indead use both sides for UDMA33 and slower,
but need to use the correct side for UDMA66+. IIRC it was related to the
different timing of signals, but I might be wrong.
Joerg
Not only timing of signals, but the encoding/decoding methodolgy
and addition of error-correction.
But the cables differ by having extra embedded ground/shield wires - 
more like SCSI,
where every second wire has always been a ground in a flat cable.

There is a decent explanation here:

http://www.interfacebus.com/Design_Connector_IDE.html

The IDE connectors did NOT originally do that - the data wires were 
side-by-side,
leading to cross-modulation with fast pulse rise times, so extra wires were
embedded, then gathered at one end and tied to 2 ground pins.

This allowed the connector to stay at 40 pins (others exist, but are 
rarely seen).
- though still only at a fraction of the allowable length for SCSI or 
SMD, let
alone DVD SCSI or HP-Parallel Current Loop.

As Matthew pointed out, the 'message' about not finding the cable (on a 
SATA port)
is superfluous/gratuitous/irrelevant.

Bill