User's Manual

LE910 V2 HARDWARE USER GUIDE 1VV0301200 Rev.2 Preliminary • 2015-08-04 45 of 81

5.5.3.3 RS232 level translation

In order to interface the LE910 V2 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: