CC864-DUAL Hardware User Guide
1vv0300791 Rev 4.4 – 2011-01-26
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights Reserved.
Page 37 of 63
3.8.1.2.
RS232C Interface and Level Translation
In order for the module to interface 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
Translate the level from 0/2.8V to +15/-15V
The RS232 UART 16450, 16550, 16650 and 16750 chipsets accept signals with
lower levels on the RS232 side (EIA/TIA-562), allowing for a lower voltage-
multiplying ratio on the level translator.
Note that the negative signal voltage must be less than 0 V so that some form 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 several available, differing in the number of drivers and receivers and
levels.
NOTE:
Always use a true RS232 level translator and
not
a translator for RS485 or
any other standard.
By convention, the driver is the level translator from the 0-3V UART level to the
RS232 level, while the receiver is the translator from RS232 level to 0-3V UART.
In order to translate the whole set of control lines of the UART, five drivers and three
receivers are required.
The figure below shows an example of level translation circuitry:
