GE866-QUAD Hardware User Guide
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Page 46 of 82
Mod. 0805 2011-07 Rev.2
9.2.
RS232 levels translation
In order to interface the GE866-QUAD 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
NOTE:
The digital input lines working at 1.8V CMOS have an absolute maximum input
voltage of 2.1V; therefore the level translator IC shall not be powered by the +3.8V
supply of the module. Instead, it must be powered from a +1.8V (dedicated) power
supply.
