GL865-DUAL V3 Hardware User Guide
1vv0301018 Rev.5 – 2013-08-05
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 41 of 76
Mod. 0805 2011-07 Rev.2
9.2.
RS232 level translation
In order to interface the GL865-DUAL V3 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.