User's Guide

LE910Cx HW User Guide
Doc#: 1VV0301298
Rev. 13.0 Page 72 of 124 2019-07-15
8.4.2. Modem Serial Port 2
On the LE910Cx, Serial Port 2 is a +1.8V UART with Rx and Tx signals only.
The UART functionality is shared with SPI, thus simultaneous use of SPI and UART is not
supported.
Table 27 lists the signals of the LE910Cx Serial Port 2.
Table 27: Modem Serial Port 2 Signals
PAD
Signal
I/O
Function
Type
Comment
D15
TXD_AUX
O
Auxiliary UART (Tx Data to DTE)
1.8V
Shared with
SPI_MOSI
E15
RXD_AUX
I
Auxiliary UART (Rx Data to DTE)
1.8V
Shared with
SPI_MISO
NOTE:
To avoid a back-powering effect, it is recommended to avoid having any
HIGH logic level signal applied to the digital pins of the module when it is
powered OFF or during an ON/OFF transition.
NOTE:
The Auxiliary UART is used as the SW main debug console. It is required to
place test points on this interface even if not used.
8.4.3. RS232 Level Translation
To interface the LE910Cx with a PC COM port or an RS232 (EIA/TIA-232) application, a
level translator is required. This level translator must perform the following actions:
• 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).