[SI-LIST] Re: Rocket I/O
- From: Mike Brown <bmgman@xxxxxxxxxx>
- To: weston_beal@xxxxxxxxxxx
- Date: Wed, 08 Sep 2004 20:44:30 -0500
I'm not a Rocket I/O expert; it's been years since I looked at it. But,
something does not add up.
If the system uses 8b-10b encoding (per Weston), there should be no
(electrical) reason for limiting the unencoded run length. The encoding will
limit the run length to 5 or less regardless of the transistions in the input
stream.
It sounds like the quoted run length spec (Greg) is for a device which does not
incorporate RLL encoding.
If the system transmits unencoded data (or data encoded with a long run-length
code) then the limitation on the run length is established by the data recovery
PLL(DLL?) which must lock onto the bit stream transitions, and the permissible
frequency error between the transmit and receive references.
I'd expect that the 75 bit run length carries perhaps a 25 PPM max frequency
error, whereas an 8b-10b encoded stream probably permits 100 PPM or greater
error. These tolerance numbers are from my experience with a vendor's IP
SerDes spec.
Mike
Beal, Weston wrote:
> Rocket I/O uses 8b10b encoding so your stream of 75 ones and 75 zeros will
> be encoded to runs of 5 and 3 ones and zeros. Now you're back closer to 620
> Mbps.
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Inchauspe, Greg E
> Sent: Wednesday, September 08, 2004 2:45 PM
> To: Sig Integ Group
> Subject: [SI-LIST] Rocket I/O
>
> The data sheet for Rocket I/O specifies a minimum data rate of
> 620 Mbps.
It also specifies a maximum of 75 transition less data bits. If I transmit a
pattern with
75 ones then 75 zeros repeating NRZ at 620 Mbps, this is equivalent to a 4 MHz
square wave.
Does this mean the Rocket I/O can do clock and data recovery on a 4 MHz square
wave signal?
> thanks,
> Greg
>
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