Table of Contents
Advertisement
IXP28XX Network Processor
RDRAM
3.2.2
Note: Designs that do not implement all channels are still required to provide power to all of the RSL I/O
3.2.3
3.2.4
3.2.5
Note: The 1.8 V and 1.5 V supplies can come up in any order before or after the 2.5 V, 1.3 V, and 3.3 V
36
Downloaded from
Elcodis.com
electronic components distributor
Unused Channel Guidelines
It is not a requirement to implement all three RDRAM channels available on the IXP28XX
network processor. However, if only a single channel is implemented it MUST be channel 0. If two
channels are implemented then they MUST be channels 0 and 1. No other channel combinations
are supported in these modes.
The unused Rambus* I/Os for unused channels do not require termination as the I/O are powered
down by default.
power pins since this is a common supply with the device.
Crosstalk
Recommendations for avoiding crosstalk are as follows:
•
Use adequate line spacing and shielding of signal vias.
— Use a 2x - 3x trace-width separation.
— Place GND vias near signal vias for a good return current path.
— Ground flood may also be used between RSL signals to minimize crosstalk. Examples of
ground floods are provided in the various Rambus* layout guides.
•
Avoid routing over plane splits and voids.
Third-party Sources
Detailed design and layout guides are available from Rambus* for short channel, RIMM, and
SO-RIMM designs; the information is not provided in this document since many third-party
vendors change information from time to time and could result in inconsistencies between the
documents. Please refer to the following third-party sources for Rambus* channel design
guidelines for the latest information:
•
Design Guides and design examples provided by Rambus*, available at www.rambus.com.
•
Design Guides for connection density provided by High Connection Density, Inc., available at
www.hcdcorp.com.
IXP28XX Network Processor Power-Up Sequence
supplies.
For Rambus* channel designs, perform the following steps to power up the IXP28XX network
processor:
1. Power up the RDRAM to 2.5 V.
— V
(1.8 V) is raised simultaneously with 2.5 V through a voltage divider.
CMOS
— Each RDRAM draws only 10 µA V
of current.
CMOS
Hardware Design Guide
Advertisement
Table of Contents
