STPC12GDYI datasheet(92/111 Pages) STMICROELECTRONICS

92 / 111 page

DESIGN GUIDELINES

92/111

Issue 1.0 - July 24, 2002

6.4. PLACE AND ROUTE

RECOMMENDATIONS

6.4.1. GENERAL RECOMMENDATIONS

Some STPC Interfaces run at high speed and

need to be carefully routed or even shielded like:

1) Memory Interface

2) PCI bus

3) Graphics and video interfaces

4) 14 MHz oscillator stage

All clock signals have to be routed first and

shielded for speeds of 27MHz or higher. The high

speed signals follow the same constraints, as for

the memory and PCI control signals.

The next interfaces to be routed are Memory, PCI,

and Video/graphics.

All the analog noise-sensitive signals have to be

routed in a separate area and hence can be

routed indepedently.

6.4.2. PLL DEFINITION AND IMPLIMENTATION

PLLs are analog cells which supply the internal

STPC Clocks. To get the cleanest clock, the jitter

on the power supply must be reduced as much as

possible. This will result in a more stable system.

Each of the integrated PLL has a dedicated power

pin so a single power plane for all of these PLLs,

or one wire for each, or any solution in between

which help the layout of the board can be used.

Powering

these

pins

with

one

Ferrite

capacitances is enough. We recommend at least

2 capacitances: one 'big' (few uF) for power

storage, and one or 2 smalls (100nF + 1nF) for

noise filtering.

Figure 6-20. Shielding signals

ground ring

ground pad

shielded signal line

ground pad

shielded signal lines

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