User's Manual

GE866-DUAL Hardware User Guide

1VV0301051 Rev. 2 – 2014-04-07

Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights

Reserved. Page 46 of 82

Mod. 0805 2011-07 Rev.2

9.2. RS232 levels translation

In order to interface the GE866-QUAD 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 CMOS have an absolute

maximum input voltage of 2.1V; therefore the level translator

IC shall not be powered by the +3.8V supply of the module.

Instead, it must be powered from a +1.8V (dedicated) power

supply.