User's Manual

GE865 Hardware User Guide
1vv0300799 Rev.11 – 13-07-2010
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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, ASC0)
MODEM SERIAL PORT 2 (Auxiliary, ASC1)
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
3.1 V
Input low level V
IL
0V
0.5V
Output high level V
OH
2.2V
3.1V