4 serial ports – Telit Wireless Solutions GM862-GPS User Manual
Page 19
GM862-GPS Hardware User Guide
1vv0300728 Rev. 0 - 27/04/06
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Right reserved
page 19 of 55
4 Serial
Ports
The serial port on the Telit GM862-GPS is the core of the interface between the module and OEM
hardware.
2 serial ports are available on the module:
• MODEM SERIAL PORT
• GPS SERIAL PORT (NMEA)
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 GPS Serial Port is a 3 wire (RX, TX GND) +2.8V UART.
The MODEM serial port on the GM862-GPS 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 GM862-
GPS UART are the CMOS levels:
Absolute Maximum Ratings -Not Functional
Parameter Min
Max
Input level on any
digital pin when on
-0.3V +3.75V
Input voltage on
analog pins when on
-0.3V +3.0
V
Operating Range - Interface levels (2.8V CMOS)
Level Min
Max
Input high level V
IH
2.1V 3.3V
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