User Guide

GM47/48 Design Guidelines
BA/SEM/MSC 02:0006 Rev PA1 18
4 Developers Board
The developers board is the reference design against which the module
has been type approved, the circuit diagram for this is available upon
request from customer support
4.1 Power Circuit
A 3A simple switcher step down voltage regulator has been used to
produce the module Vcc. Two 6800µF capacitors are located adjacent
to the module to cope with the GSM current pulses. The capacitors are
low ESR type approximately 16mΩ.
4.2 SIM Circuit
The SIM holder has been connected directly to the module, the
SIMVCC decoupling capacitor has been omitted and should be present
for all designs.
Note: Provision was made for additional ESD protection on the board
for development purposes.
This is not required and the devices have been removed from the
SIMDATA and SIMCLK signals to minimise capacitance on these
lines.
4.3 On/Off switch
The on/off line is connected to a momentary contact switch, this
ensures correct operation of the alarm clock feature in the module.
4.4 Programming circuitry
The data lines are converted between 2.7V & 5V logic and then
between 5V & RS232 levels. The data signal into the module is
powered from the VIO supply interface which ensures isolation of the
signal when the module is off.
To invoke programming mode the jumper JP27 is used. The Vppflash
signal path is no longer used.