ME910C1 mPCIe HW Design Guide
1VV0301642 Rev. 2 Page 32 of 56 2022-01-14
For minimum implementations, only the TXD and RXD lines
need to be connected. The other lines can be left open if the host
software allow it and is correctly set.
RS232 Level Translation
To interface the ME910X1-mPCIe UART with a RS232 PC COM Port, a voltage level
translator is required. This level translator must:
• Invert the electrical signal in both directions
• Change the level from V
IO
level to RS232 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 therefore 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 UART V
IO
, in our case V
IO
=1.8V,
to the RS232 level. The receiver is the translator from the RS232 levels to V
IO
levels of the
UART.
To translate the whole set of control lines of the UART, the following is required:
• 1 driver
• 1 receiver
The digital input lines operate at 1.8V CMOS.
Use a level voltage translator to correctly interface to them.
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