AN_SC1x3_Design_Guide_V10.PDF
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» Application Note
Design Guide for SC1x3
Designing hardware around a SC123 or it’s variants can be easier than for most
other embedded systems with a similar level of functionality, but it isn’t always
easy.
There are many points that can be forgotten or not be considered what makes a
initial operation very difficult.
This document wants to show important points and answers to some questions
which comes up when designing schematic and layout. It is an addon to the
Design Giude for SC1x
. Most of the hints and rules of
Design Giude for SC1x
apply also for SC1x3. Please read
Design Giude for SC1x
before you read this.
1. Signals UCSIN# / UCSOUT#
Those signals are belong to one of the most important signals. If you don’t
want to use a external memory to map it into SC1x3’s internal memory,
don’t
forget the connection between those signals
.
If UCSIN# is left open and without any external logic, the system won’t boot.
2. Crystal
Use a 25MHz crystal with 100ppm max., no 24.576MHz or similar crystals.
You can use an oscillator with 25MHz and connect it to XIN of the SC1x3,
then XOUT can be left open.
3. CPUCLK
This signal is the most sensitive signal of the SC1x3. For a steady boot up a
feedback line between XOUT and CPUCLK is necessary (see HW Manual).
4. 3,3V and A3,3V V
DD
(VDD1A, VDD2A, VSS3A, VSS4A)
Seperate the two different power supplies through a ferrite and corresponding
layout. The power supply for the internal PHY of the SC1x3 has to be
seperated from the digital power supply to decouple distortions. Use a
additional ferrite for CPUCLK signal to XOUT for the same reason. Otherwise
the 96MHz cpu clock could disturb the ethernet signal.
5. Testpoints
The SC1x3 is a BGA. So, all balls that are
not
connected and
not
routed to
an outer layer of the motherboard are unusable for this hardware
forever
. If
you are not sure if you need a signal in future or not, or you don’t understand
the function of some balls, then use testpoints! Connect testpoints for
measuring and evaluating in your first design. “If anything can go wrong, it
will”
. If you have some testpoints connected to the right signals you can try it
out, before you redesign the hardware.
6. Startup Configuration of SC1x3
The SC1x3 can be configured before any software runs through some pullup-
/down resistors at the address signals. These external resistors are not
necessary, if
nothing
is connected to
these
signals (except testpoints). If you
are connecting anything to this address line, you should place the resistor for
the desired configuration or predefined state, because any device can
overwrite the internal weak resistors.
1
Murphy’s Law