User's Manual

LE920A4 HW User Guide Application Guide
Doc#: 1VV0301261 Download and Debug Port
Rev. 4.3 Page 106 of 123 2017-12-07
Pad Signal I/O Function Contact Air
Antenna
AD1,AU9,S1 Antenna
pads
Analog
I/O
Antenna pad ± 4KV ± 8KV
Appropriate series resistors must be considered to protect the input lines from
overvoltage.
Download and Debug Port
This section provides recommendations for the design of the host system for downloading
or upgrading the Telit software and for debugging the module when it is already mounted
on a host system.
• For downloading or upgrading the Telit software:
Updating the firmware by the host is only possible via USB and not via UART.
If the USB interface is not used, it is highly recommended to place an optional
USB connector on the application board. At the minimum, test points of the USB
signals are required to enable SW update.
• For debugging the module:
USB and Auxiliary UART interfaces are used for debugging the module. If the USB
and AUX UART interfaces are not used, it is highly recommended to place optional
connectors on the application board. At least, test points of the USB and AUX
UART signals are required for debugging purposes.
11.5.1. Fast Boot Mode
Fast Boot mode is normally used by Telit software to enter SW Download mode.
Fast Boot mode is triggered by GPIO_20 (PAD AN4). Asserting this signal high (1.8V)
during boot will force the system into Fast Boot mode.
11.5.2. Recovery Boot Mode
A Recovery Boot Download mode is used if a corrupted boot image was flashed into the
device or if all other recovery modes failed.
Recovery Boot Download mode is triggered by the WCI_RX signal (PAD AT2). Asserting
this signal high (1.8V) during boot will force the system into Recovery Boot Download
mode.