User's Manual

LE910 Hardware User Guide
1vv0301089 Rev.7 – 25-10-2015
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 58 of 88
11.3 RS232 level translation
In order to interface the LE910 with a PC com port or a RS232 (EIA/TIA-232) application a
level translator is required. This level translator must:
 invert the electrical signal in both directions;
 Change the level from 0/1.8V to +15/-15V.
Actually, the RS232 UART 16450, 16550, 16650 & 16750 chipsets accept signals with lower
levels on the RS232 side (EIA/TIA-562), allowing a lower voltage-multiplying ratio on the level
translator. Note that the negative signal voltage must be less than 0V and hence some sort of
level translation is always required.
The simplest way to translate the levels and invert the signal is by using a single chip level
translator. There are a multitude of them, differing in the number of drivers and receivers and in
the levels (be sure to get a true RS232 level translator not a RS485 or other standards).
By convention the driver is the level translator from the 0-1.8V UART to the RS232 level. The
receiver is the translator from the RS232 level to 0-1.8V UART.
In order to translate the whole set of control lines of the UART you will need:
 5 drivers
 3 receivers
NOTE:
Avoid any overvoltage condition on digital pins.
VAUX can be used (always active during LE910 operation) for any level translation or
pullup/pulldown on digital pins.