Specifications

Rev 1.0 1/27/14 30
30
Reference Guide
Interfaces
Parameter
I/O
Min
Typ
Max
Unit
Input Low
0
0.01
V
Output High
0.36
0.38
0.44
V
Output Low
0
0.01
V
The USB feature can be activated by using the AT+WMFM=0,1,3 AT command.
Refer to the AT Commands Interface Guide at http://www.usr.com/support/3500 for
more information regarding this AT command.
3.2. Back Interface
Figure 21. USR3500 Back Interface
3.2.1. SIM Interface
A SIM card can be directly connected to the USR3500 through the embedded SIM
socket. This interface controls 3V / 1V8 SIM cards and it is fully compliant with GSM
11.11 recommendations concerning SIM functions.
The SIM interface of the USR3500 is ESD protected. Transient overvoltage
protections in ESD are internally added on the signals connected to the SIM interface
in order to prevent any damage from electrostatic discharge.
The SIM interface uses 5 SIM signals, namely:
• SIM-VCC: SIM Power supply
• ~SIM-RST: Reset
• SIM-CLK: Clock
• SIM-IO: I/O Port
• SIMPRES: SIM card detection
Secondary RF Interface
SIM Interface
Main RF Interface
LED Status Indicator
Expansion Compartment
GPS RF Interface