User's Guide

LE940B6 HW User Guide
Rev. 2.02
Page 74 of 111 2020-01-10
Serial Ports
The serial port is typically a secondary interface between the LE940B6 module and OEM
hardware. The following serial ports are available on the module:
• Modem Serial Port 1 (Main)
• Modem Serial Port 2 (Auxiliary)
• Modem Serial Port 3 (GNSS)
Several serial port configurations can be designed for the OEM hardware. The most
common are:
• RS232 PC com port
• Microcontroller UART @ 1.8V (Universal Asynchronous Receive Transmit)
• Microcontroller UART @ 3.3V/5V or other voltages different from 1.8V
Depending on the type of serial port on OEM hardware, level translator circuits may be
needed to make the system operate. The only configuration that does not need level
translation is the 1.8V UART. The LE940B6 UART has CMOS levels as described in
Section 4.3.1, 1.8V Standard GPIOs.
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 25 lists the signals of
LE940B6 Serial Port 1.
Table 25: 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
Provided to Dekra under NDA
Distribution is Prohibited except for
Dekra employees with a Need to know