STPCC5HEBC STMicroelectronics, STPCC5HEBC Datasheet - Page 78

• Manufacturer Part Number: STPCC5HEBC
• Description: IC SYSTEM-ON-CHIP X86 388-PBGA
• Manufacturer: STMicroelectronics
• Series: -r

Specifications of STPCC5HEBC

• Applications: Set-Top Boxes, TV
• Core Processor: x86
• Program Memory Type: External Program Memory
• Controller Series: STPC® Consumer-II
• Ram Size: External
• Interface: EBI/EMI, I²C, IDE, ISA, Local Bus
• Number Of I /o: -
• Voltage - Supply: 2.45 V ~ 3.6 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Not Compliant

DESIGN GUIDELINES
6.4.3. MEMORY INTERFACE
6.4.3.1. Introduction
In order to achieve SDRAM memory interfaces
which work at clock frequencies of 100 MHz and
above, careful consideration has to be given to the
timing of the interface with all the various electrical
and physical constraints taken into consideration.
The guidelines described below are related to
SDRAM components on DIMM modules. For
applications where the memories are directly
soldered to the motherboard, the PCB should be
laid out such that the trace lengths fit within the
constraints shown here. The traces could be
slightly shorter since the extra routing on the
6.4.3.3. Board Layout Issues
The physical layout of the motherboard PCB
assumed in this presentation is as shown in
6-19. Because all of the memory interface signal
balls are located in the same region of the STPC
device, it is possible to orientate the device to
reduce the trace lengths. The worst case routing
length to the DIMM1 is estimated to be 100 mm.
Solid power and ground planes are a must in order
to provide good return paths for the signals and to
reduce EMI and noise. Also there should be ample
high frequency decoupling between the power
78/93
CONTROLLER
SDRAM
PLL
PLL
Figure 6-18. Clock Scheme
Release 1.5 - January 29, 2002
MCLKO
MCLKI
MA[ ] + Control
MD[63:0]
Figure
DIMM PCB is no longer present but it is then up to
the user to verify the timings.
6.4.3.2. SDRAM Clocking Scheme
The SDRAM Clocking Scheme deserves a special
mention here. Basically the memory clock is
generated on-chip through a PLL and goes
directly to the MCLKO output pin of the STPC. The
nominal frequency is 100 MHz. Because of the
high load presented to the MCLK on the board by
the DIMMs it is recommended to rebuffer the
MCLKO signal on the board and balance the skew
to the clock ports of the different DIMMs and the
MCLKI input pin of STPC.
and ground planes to provide a low impedance
path between the planes for the return paths for
signal routings which change layers. If possible,
the traces should be routed adjacent to the same
power or ground plane for the length of the trace.
For the SDRAM interface, the most critical signal
is the clock. Any skew between the clocks at the
SDRAM components and the memory controller
will impact the timing budget. In order to get well
matched
recommended that all the DIMM clock pins, STPC
clocks
at
all
components
it
is