HE920 Hardware User Guide
1vv0301014 Rev.9 – 2014-01-23
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved.
Page 52 of 84
9.
Serial Ports
The serial port on the Telit HE920 is the interface between the module and OEM hardware.
2 serial ports are available on the module:
MODEM SERIAL PORT 1(Main)
MODEM SERIAL PORT 2 (Auxiliary)
Several configurations can be designed for the serial port on the OEM hardware.
The most common are:
RS232 PC com port;
microcontroller UART @ 1.8V (Universal Asynchronous Receive Transmit) ;
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 HE920 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 HE920 UART are the CMOS levels:
Absolute Maximum Ratings -Not Functional
Parameter
HE920
Min
Max
Input level on any
digital pin when on
-0.3V
+2.7V
Input voltage on
analog pins when on
-0.3V
+2.7 V
Operating Range - Interface levels
Level
HE920
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
