On Sat, 10 Jan 2009 19:19:29 -0500, Paul put
finger to keyboard and composed:

Franc Zabkar wrote:
On Sat, 10 Jan 2009 06:57:06 -0800 (PST), "larry moe 'n curly"
put finger to keyboard and composed:

I have some motherboards designed for 4-6 SATA ports, but only 2 SATA
connectors were installed, and I'd like to add the missing connectors
plus any needed termination resistors.
Here's an example with an ECS GeForce 6100SM-M v. 1.0 motherboard:

http://farm4.static.flickr.com/3397/...b349938d_o.jpg

What are the values of the missing resistors? I thought that each
pair of SATA data lines needed one 100 ohm resistor between them, but
on this circuit board the resistors seem to be arranged differently.

The "resistors" at the SATA4 connector appear to be labelled as
C151-4. This begs the question, what are caps doing on a high speed
interface?

This URL talks about 100 ohm termination resistors across the two
signal pairs:
http://www.interfacebus.com/Design_C...erial_ATA.html

This URL suggests that 20K pullup and pulldown resistors may sometimes
be used in noisy environments:
http://www.interfacebus.com/Design_Connector_RS644.html

- Franc Zabkar

I could find a reference to AC or DC coupling here. (I bet
some sata-io.org document would cover this in more detail.)

http://www.atmel.com/dyn/resources/p...ents/3527s.pdf

I have an Intel sample schematic where the 1.5Gb/sec SATA interface
was DC coupled. And can also find examples with AC coupling.

Pg. 8 here uses 10nF capacitors.

http://pdfserv.maxim-ic.com/en/ds/MAX4951.pdf

PCI Express uses AC coupling, and also uses 8B10B coding
like SATA does. At least with PCI Express, coupling caps
are used consistently.

Paul

Thanks again. I'd always thought AC coupling wasn't necessary when the
two devices at either end of the cable were differentially coupled or
powered from the same supply. I tend to associate AC coupling with
analogue circuits rather than digital.

- Franc Zabkar
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