[SI-LIST] Re: SDRAM PCB Layout
- From: Gene Glick <gglick@xxxxxxxxxxxx>
- To: Stephen Zinck <szinck1@xxxxxxxxxxxx>
- Date: Fri, 30 Apr 2010 11:01:16 -0400
On 4/30/2010 1:01 AM, Stephen Zinck wrote:
> Hi Gene,
>
> I am not sure whether the Atmel device provides you with output
> drive-strength control or not.
Looks like the termination resistors are necessary. This is right from
the data sheet (errata):
43.2.5.1 I/O High Drive Strength
The I/O output buffer drive is too high to guarantee the timings. This
is applicable to the External Bus Interface signals and to the
peripheral I/Os. This leads to fast rise and fall time when the signals
change, causing high currents to be drawn on the power supply pins and
leads to emission of high frequencies. This may affect the operation of
the device and may result in the emission of radio-frequency signals,
making EMC certification difficult.
Problem Fix/Workaround
It is strongly recommended:
• to place the memories connected to the EBI as close as possible to the
SAM9260 on the PCB
• to route all the EBI signals with a series resistor, typical value 33 ohms
• to adjust the series resistor value with tools taking into account the
IBIS model of the pads and the characteristics of the wires of the PCB,
in order to guarantee rise and fall times as long as timings permit.
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