AN2536 Freescale Semiconductor / Motorola, AN2536 Datasheet - Page 16

• Manufacturer Part Number: AN2536
• Description: MC9328MX1 and MC9328MXL High Speed Layout Design Guidelines
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
MC9328MX1/MXL Case Study
capacitance no larger than 20pF. With ADS ver 1.1, a standard memory test program is executed (refer to
Section 5, “References,” on page 22). It shows smooth execution up to 96 MHz with a 3.0V memory bus
(0–70 degrees). In an experiment to test bus speed at 1.8V, 1.8V SDRAM was placed on a separate board
connected to the SODIMM connector and it was found to operate stable up to 86 MHz. However, it should
be noted that adding memories via the SODIMM connector increases both trace length and bus loading.
Section 3.2, “MC9328MX1 Demo v0.1,” will address this issue with the design of a PDA form factor
style board.
3.2 MC9328MX1 Demo v0.1
With the ADS ver 1.1, we found the memory access at 96 MHz unstable at 1.8V. In order to achieve the
system stability at 96 MHz with a 1.8V bus, the memories should be placed on the same PCB as close as
possible to the MC9328MX1/MXL and not on a separate PCB connected via the SODIMM. This will
improve the setup time of the memory bus. A PDA form factor board following this guideline was created
and in this trial, we observed the R, L, and C are greatly improved. Figure 24 provides a picture of the form
factor PCB and illustrates the memory configuration (two 16-bit SDRAMs and one 32-bit Disk On Chip
(DOC)). While Figure 25 lists the PCB layer description. Figure 26 on page 17 provides details of the
memory devices capacitive loading, and Figure 27 on page 17 shows the PDA form factor design in its
casing. Figure 28 on page 18 details the simulation data and the characteristics of the worst case signals
from Address, Data and Control traces relative to the SDCLK trace, provided by the board vendor.
Figure 24. MC9328MX1 Demo v0.1 PCB Illustrating the Memory Layout:
2x16-bit SDRAMs and 1x32-bit DOC
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MC9328MX1/MXL Application Note
MOTOROLA
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