User Guide

ME910G1 Preliminary HW Design Guide
1VV0301593 Rev.2 Page 54 of 95 2020-01-13
NOTE:
Due to the shared functions, TX_AUX/RX_AUX port and SPI port
cannot be used simultanously.
In order to avoid a back powering effect it is recommended to avoid
having any HIGH logic level signal applied to the digital pins of the
ME910G1 when the module is powered off or during an ON/OFF
transition.
Refer to ME910G1 series AT command reference guide for port
configuration.
5.7.3.3. RS232 level translation
In order to interface the ME910G1 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