Jackson Labs LTE-Lite, User Manual

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LTE-Lite User Manual
20 © 2020 Jackson Labs Technologies, Inc.
2.3.10 Module Serial IO pins
The LTE-Lite module supports three individual serial port pins. Two of these are directly connected
to the internal microcontroller (pin 12 RXD_CPU, and pin 14 TXD_CPU), and one is directly
connected to the GPS receiver on the module (pin 13 TXD_GPS). Due to only having a single serial
port on the microcontroller that needs to be used for both GPS receiver initialization and monitoring
as well as external communications and In System Programming (ISP) the microcontroller serial port
is connected to both the internal GPS receiver and external USB chip.
The output TXD signal of the microcontroller is thus connected to the GPS serial port input pin, and
the USB serial port input pin.
The input RXD signal of the microcontroller is connected to the GPS serial port output pin with a
2.7K Ohms series resistor, and to the USB serial port transmit pin via switch SW3 on the evaluation
board. This allows the GPS receiver to send NMEA serial information to the microcontroller during
normal operation, and allows the USB chip to drive the microcontroller serial receive input during
ISP communications by over-driving the signal that the GPS receiver is sending to the
microcontroller. The user only needs to use the microcontroller serial output transmit pin 14 for
oscillator lock status output, and the GPS receiver serial output transmit pin 13 for normal operation
as the ISP mode is only supported at the JLT factory.
The GPS receiver can generate NMEA sentences in either 1Hz or 5Hz update rate depending on the
rate-selection pin 11 (default is internally pulled-up for 1Hz update rate).
2.3.11 Module IO Pinout
The LTE-Lite SMT Module has 32 SMT pads arranged in a standard IC pinout pattern. The
following drawing shows the pinout of the module.
Figure 2.13 Pinout of the LTE-Lite SMT Module (Top View)