HE910 Hardware User Guide
1VV0300925 Rev. 32 Page 82 of 111 2019-11-25
RS232 level translation
In order to interface the HE910 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).
Figure 12-2 RS232 Level
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