User's Guide

HE863 Family Hardware User Guide
1vv0300891 Rev.5
- 2011-03-18
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights
Reserved. Page 83 of 89
15. SIM holder design guide
15.1. Overview
In HE863 Family modules there are five pins for SIM card holder
connection.
These lines are:
SIMVCC (SIM Power supply)
SIMRST (SIM Reset)
SIMIO (SIM Data)
SIMIN (SIM Presence/Absence) (TBD)
SIMCLK (SIM Clock)
SIM connection must take in account of three key issues:
1) Data Integrity: standard rules for digital layout and
routing must be followed taking in consideration that SIMCLK
has frequency of 3.57 MHz and SIMIO has 9600Bps baud rate.
2) EMI/EMC: this is a key aspect to consider designing an
application based on TELIT modules with internal antenna and/or
without a proper-shielded box.
Some of these conditions may occur:
- Antenna picks-up digital noise coming from SIM card lines.
- Antenna radiated field may interfere digital lines.
- Digital lines (in particular clock) may radiate spurious in
the surrounding space.
To overcome all these potential problems, connection lines must
be kept as short as possible and shielded.
SIM-holder position has to be as far as possible from antenna.
RF bypass capacitors (10pF...33pF) closed to SIM card SIM-
holder are another good care.
When connection is not short, insertion of 10..100ohm resistor
with 10..33pF capacitor (RC filter) is a good caution to
improve EMI from SIMCLK line.
Do not insert resistor on SIMVCC, SIMRST and SIMIO lines, their
use is not supported by SIM electrical interface.
3) ESD: take standard ESD caution if application based on TELIT
module has SIM holder with contacts reachable from human body.