GE865 Hardware User Guide
1vv0300799 Rev.9 – 27-07-2009
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 37 of 70
9 Serial Ports
The serial port on the GE865 is the core of 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 (AUX)
9.1 MODEM SERIAL PORT
Several configurations can be designed for the serial port on the OEM hardware, but
the most common are:
•
RS232 PC com port
•
microcontroller
UART
@
2.8V - 3V (Universal Asynchronous Receive Transmit)
•
microcontroller
UART
@
5V or other voltages different from 2.8V
Depending from 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 doesn't need a
level translation is the 2.8V UART.
The serial port on the GE865 is a +2.8V UART with all the 7 RS232 signals. It differs
from the PC-RS232 in the signal polarity (RS232 is reversed) and levels. The levels for
the GE865 UART are the CMOS levels:
Absolute Maximum Ratings -Not Functional
Parameter
Min
Max
Input level on any
digital pad when on
-0.3V
+3.1V
Input voltage on
analog pads when on
-0.3V
+3.1V
Operating Range - Interface levels (2.8V CMOS)
Level
Min
Max
Input high level V
IH
2.1V
3.0 V
Input low level V
IL
0V
0.5V
Output high level V
OH
2.2V
3.0V
Output low level V
OL
0V
0.35V