NL865B1 HW Design Guide
1VV0301450 Rev. 1
Page
42
of
72
2017-11-20
5.5.1.3.
RS232 LEVEL TRANSLATION
In order to interface the NL865B1 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.
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).
