Product Info

LTE Module Series
EC21 Hardware Design
EC21_Hardware_Design
3-31
/ 105
3.4.1.3. USB Application with USB Suspend/Resume and RI Function
If the host supports USB suspend/resume, but does not support remote wake-up function, the RI signal is
needed to wake up the host.
There are three preconditions to let the module enter into the sleep mode.
 Execute AT+QSCLK=1 command to enable sleep mode.
 Ensure the DTR is held at high level or keep it open.
 The host’s USB bus, which is connected with the module’s USB interface, enters into suspended
state.
The following figure shows the connection between the module and the host.
Figure 5: Sleep Mode Application with RI

Sending data to EC21 through USB will wake up the module.

When EC21 has a URC to report, RI signal will wake up the host.
3.4.1.4. USB Application without USB Suspend Function
If the host does not support USB suspend function, USB_VBUS should be disconnected via an additional
control circuit to let the module enter into sleep mode.

Execute AT+QSCLK=1 command to enable sleep mode.

Ensure the DTR is held at high level or keep it open.

Disconnect USB_VBUS.
The following figure shows the connection between the module and the host.