User's Guide

UL865 Hardware User Guide
1VV0301050 Rev 2 – 2013-10-09
The serial port on the UL865 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)
Several configurations can be designed for the serial port on the OEM hardware, but the most
common are:
RS232 PC com port
microcontroller UART @ 1.8V (Universal Asynchronous Receive Transmit)
microcontroller UART @ 3V or other voltages different from 1.8V
microcontroller UART @ 5V or other voltages different from 1.8V
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 1.8V UART.
The serial port on the UL865 is a +1.8V UART with all the 8 RS232 signals. It differs from
the PC-RS232 in the signal polarity (RS232 is reversed) and levels. The levels for the UL865
UART are the CMOS levels:
Absolute Maximum Ratings -Not Functional
Parameter
Min
Max
Input level on any digital
pad when on
-0.3V
+2.1V
Operating Range - Interface levels (1.8V CMOS)
Level
Min
Max
Input high level V
IH
1.5V
1.9V
Input low level V
IL
0V
0.35V
Output high level V
OH
1.6V
1.9V
Output low level V
OL
0V
0.2V