User's Manual

DE910 Series Hardware User Guide
1vv0301183 Rev.1 – 2015-2-13
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Reserved. Page 46 of 70
NOTE:
According to V.24, RX/TX signal names are referred to the application side. Therefore, on the
DE921 side these signals are in the opposite direction: TXD on the application side will be
connected to the receive line (here named TXD/ rx_uart) of the DE921 serial port and vice
versa for RX.
NOTE:
High-speed UART supports up to 4Mbps. Please refer to the AT command User Guide in
detail.
WARNING:
Consider a mechanical design and a low-capacitance ESD protection device to protect DE921
or customer specific requirements from ESD event to UART port.
8.2. Modem Serial Port 2
Serial port 2 on the DE921 is a +1.8V UART with only the RX and TX signals.
The signals of the DE921 serial port are:
Pin Signal I/O Function Type
A13
TXD2 O Auxillary UART (TX Data to DTE) 1.8V
A11
RXD2 I Auxillary UART (RX Data from DTE) 1.8V
NOTE:
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 DE921 when the module is powered off or during
an ON/OFF transition.
8.3. RS232 Level Translation
In order to interface the Telit DE921 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 +/-15V