LE910C1
Hardware User Guide
1VV0301298 Rev. 1.08 - 2017-11-14
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8.4.3.
RS232 Level Translation
To interface the LE910C1 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
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.
To translate the whole set of control lines of the UART, the following is required:
•
2 drivers
•
2 receivers
NOTE:
The digital input lines operating at 1.8V CMOS have an absolute maximum input voltage of 2.7V.
Therefore, the level translator IC must not be powered by the +3.8V supply of the module. Instead,
it must be powered from a ded1.8V power supply.
An example of RS232 level adaption circuitry could use a MAXIM transceiver (MAX218).
In this case, the chipset is capable of translating directly from 1.8V to the RS232 levels (Example on
4 signals only).
Figure 13: RS232 Level Adaption Circuitry Example
