User's Manual

UE866 HARDWARE USER GUIDE 1vv0301157 Rev.7 • 2015-04-17 38 of 68

RS232 LEVEL TRANSLATION

In order to interface the UE866 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

An example of RS232 level adaptation circuitry could be done using a MAXIM transceiver (MAX218)

In this case the chipset is capable to translate directly from 1.8V to the RS232 levels (Example done

on 4 signals only).

The RS232 serial port lines are usually connected to a DB9 connector with the following layout: