User's Manual

LTE Module Series
EC21 Hardware Design
EC21_Hardware_Design Confidential / Released 57 / 94
3.19. USB_BOOT Interface
EC21 provides a USB_BOOT pin. During development or factory production, USB_BOOT pin can force
the module to boot from USB port for firmware upgrade.
Table 23: Pin Definition of USB_BOOT Interface
Pin Name Pin No. I/O Description Comment
USB_BOOT 115 DI
Force the module to boot from USB
port
1.8V power domain.
Active high.
If unused, keep it open.
The following figure shows a reference circuit of USB_BOOT interface.
Figure 30: Reference Circuit of USB_BOOT Interface