User's Manual
HC864-AUTO Hardware User Guide
1vv0300946 Rev.4 – 2012-12-27
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 42 of 77
8. Serial Ports
The serial port on the Telit HC864-AUTO is the interface between the module and OEM
hardware.
2 serial ports are available on the module:
• MODEM SERIAL PORT;
• MODEM SERIAL PORT 2 (DEBUG).
NOTE:
In order to avoid a back powering effect it is recommended to avoid having any HIGH logic
level signal applied to the digital pins of the module when is powered OFF or during an
ON/OFF transition.
8.1. Modem Serial Port
Several configurations can be designed for the serial port on the OEM hardware.
The most common are:
• RS232 PC com port;
• microcontroller UART @ 2.6V (Universal Asynchronous Receive Transmit) ;
• microcontroller UART @ 5V or other voltages different from 2.6V.
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 2.6V UART.
The serial port on HC864-AUTO is a +2.6V UART with all the 7 RS232 signals. It differs
from the PC-RS232 in signal polarity (RS232 is reversed) and levels.