User's Manual

GL865 Hardware User Guide
1vv0300910 Rev.1 – 2011-07-22
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 41 of 79
9. Serial Ports
The serial port on the GL865 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)  for AT commands and Data
MODEM SERIAL PORT 2 (AUX)  for AT commands or Debug
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 GL865 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
GL865 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 hi
gh level
VIH
2.1V 3.1 V
Input low level
VIL
0V 0.5V
Output high level
VOH
2.2V 3.1V
Output low level
VOL
0V 0.35V