L
LE920 Hardware User Guide
1vv0301026 Rev.0 - draft4 – 2013-05-
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 50 of 76
9.
Serial Ports
The serial port on the Telit LE920 is the interface between the module and OEM hardware.
Two serial ports are available on the module:
x
MODEM SERIAL PORT 1(Main)
x
MODEM SERIAL PORT 2 (Auxiliary) -TBD
Several configurations can be designed for the serial port on the OEM hardware.
The most common are:
x
RS232 PC com port;
x
Microcontroller UART @ 1.8V (Universal Asynchronous Receive Transmit) ;
x
Microcontroller UART @ 5V or other voltages different from 1.8V.
Depending on the type of serial port on the OEM hardware, a level translator circuit may be
needed to make the system work. The only configuration that does not need a level translation
is the 1.8V UART.
The serial port 1 on LE920 is a +1.8V UART with all the 7 RS232 signals. It differs from the
PC-RS232 in signal polarity (RS232 is reversed) and levels.
The Serial port 2 is a +1.8V Auxiliary
UART.
The levels for LE920 UART are the CMOS levels:
Absolute Maximum Ratings -Not Functional
Parameter
LE920
Min
Max
Input level on any
digital pin when on
-0.3V
+2.16 V
Input voltage on
analog pins when on
-0.3V
+2.16 V
Operating Range - Interface levels
Level
LE920
Min
Max
Input high level
1.5V
2.1V
Input low level
-0.3V
0.5V
Output high level
1.35V
1.8V
Output low level
0V
0.45V
