Rev 1.9.1 Feb.09
Proprietary and Confidential
67
In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.
USIM operation
Note: For interface design
requirements, refer to:
(2G) 3GPP TS 51.010-1, section
27.17, or
(3G) ETSI TS 102 230 V5.5.0,
section 5.2
When
designing
the
remote
USIM
interface,
you
must
make
sure
that
the
USIM
signal
integrity
is
not
compromised.
Some
design
recommendations
include:
•
The
total
impedance
of
the
VCC
and
GND
connections
to
the
USIM,
measured
at
the
module
connector,
should
be
less
than
1
Ω
to
minimize
voltage
drop
(includes
any
trace
impedance
and
lumped
element
components
—
inductors,
filters,
etc.).
Note: The MC87xx is designed for use with either a 1.8 V or 3 V
USIM.
•
Position
the
USIM
connector
no
more
than
10
cm
from
the
module.
If
a
longer
distance
is
required
because
of
the
design
of
the
host
device,
a
shielded
wire
assembly
is
recommended—connect
one
end
as
close
as
possible
to
the
USIM
connector
and
the
other
end
as
close
as
possible
to
the
module
connector.
The
shielded
assembly
may
help
shield
the
USIM
interface
from
system
noise.
•
Reduce
crosstalk
on
the
XIM_data
line
to
reduce
the
risk
of
failures
during
GCF
approval
testing.
•
Avoid
routing
the
XIM_CLK
and
XIM_DATA
lines
in
parallel
over
distances
greater
than
2
cm—cross
‐
coupling
of
these
lines
can
cause
failures.
•
Keep
USIM
signals
as
short
as
possible,
and
keep
very
low
capacitance
traces
on
the
XIM_DATA
and
XIM_CLK
signals
to
minimize
signal
rise
time—signal
rise
time
must
be
<1
μ
s.
High
capacitance
increases
signal
rise
time,
potentially
causing
your
device
to
fail
certification
tests.
•
Add
external
pull
‐
up
resistors
(15
k
Ω
—
30
k
Ω
),
if
required,
between
the
SIM_IO
and
SIM_VCC
lines
to
optimize
the
signal
rise
time.
•
3GPP
has
stringent
requirements
for
I/O
rise
time
(<1
μ
s),
signal
level
limits,
and
noise
immunity—consider
this
carefully
when
developing
your
PCB
layout.
•
The
VCC
line
should
be
decoupled
close
to
the
USIM
socket.
•
USIM
is
specified
to
run
up
to
5
MHz
(USIM
clock
rate).
Take
note
of
this
speed
in
the
placement
and
routing
of
the
USIM
signals
and
connectors.
•
You
must
decide
if,
and
how
much
,
additional
ESD
protection
and
series
resistors
are
suitable
for
your
product.
The
MC87xx
already
includes
additional
ESD
protection.
Adding
more
protection
(additional
circuits)
than
is
