User's Manual

LE910 Hardware User Guide

1vv0301089 Rev.3 – 09-06-2014

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:

The digital input lines working at 1.8V have an absolute maximum input voltage of 2.7V;

therefore the level translator IC shall not be powered by the VBATT supply of the module to

avoid damaging the LE910 digital signals.

Instead it has to be supplied by a dedicated 1.8V power supply.