Fibocom MG661-EU - I2 C

3 Application Interfaces
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3.2.4 Download
The MG661 module supports USB download function. To enter the download mode, it is
necessary to pull down USB_BOOT to ground or pull up to VDD_EXT, and then power on or
reset the module. The module will enter the download mode. It is recommended to pull down
USB_BOOT to ground to enter the download mode.
In the download mode, the module can be upgraded by the software through the USB
interface. The following figure shows the reference circuit.
Figure 12. Reference circuit for entering the download mode
It is recommended to add 1k resistor and TVS tube near the module.
3.3 Baseband Interface
For details about how to use the GPIO multiplexing function of MG661 Open models, see
Fibocom_MG661_GPIO Function Multiplexing Table.
3.3.1 USB 2.0
Background
USB (Universal Serial Bus) is an external bus standard used to regulate the connection and
communication between computers and external devices. It is the interface technology
applied in PC field. USB is generally used for debugging, or for software upgrades.