User's Manual

LE940B6 Hardware User Guide
1VV0301331 Rev. 1.8 - 2017-03-15
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8.2.1. Modem Serial Port 1
Serial Port 1 is a +1.8V UART, having all the 8 RS232 signals. It differs from the PC-RS232 in the
signal polarity (RS232 is reversed) and levels. Table 26 lists the signals of LE940B6 Serial Port 1.
Table 26: Modem Serial Port 1 Signals
RS232 Pin # Signal Pad No. Name Usage
1 DCD -
DCD_UART
AE18 Data Carrier
Detect
Output from LE940B6 that
indicates carrier presence
2 RXD -
TX_UART
AF19 Transmit line
*see Note
Output transmit line of LE940B6
UART
3 TXD -
RX_UART
AH19 Receive line
*see Note
Input receive line of LE940B6 UART
4 DTR -
DTR_UART
AC18 Data Terminal
Ready
Input to LE940B6 that controls the
DTE READY condition
5 DSR -
DSR_UART
AG18 Data Set Ready Output from LE940B6 that
indicates that the module is ready
6 RTS -
RTS_UART
AA18 Request to Send Input to LE940B6 controlling the
Hardware flow control
7 CTS -
CTS_UART
AK19 Clear to Send Output from LE940B6 controlling
the Hardware flow control
8 RI -
RI_UART
AJ18 Ring Indicator Output from LE940B6 indicating
the Incoming call condition
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:
For minimum implementations, only the TXD and RXD lines need be connected. The other lines
can be left open provided a software flow control is implemented.
NOTE:
According to V.24, Rx/Tx signal names refer to the application side; therefore, on the LE940B6
side, these signal are in the opposite direction: TXD on the application side will be connected to
the receive line (here named TXD/ RX_UART) of the LE940B6 serial port and vice versa for Rx.