Quectel UC20 Application Note page 11

When you power on module, if you use the UART, baud rate of the UART must be fixed by
AT+IPR=115200&W. Before using ATD*99# to set up PPP, you must check the status of SIM card with
AT+CPIN?. When SIM card is OK, you also need to check the state of network periodically with
AT+CREG? and AT+CGREG? until network condition is ready.
NOTES
1. Ensure that MCU and the module are synchronized successfully after rebooting the module. MCU
sends "AT<CR><LF>" to module every 100ms until "OK" is received from the module. And if the
UART is used, MCU fixes and saves baud rate by "AT+IPR=xxx&W" after synchronization is
successful.
2. Please note that MCU has to wait for the response (for example OK, CME error, CMS error) of the
previous AT command before inputting the next AT command. The module can be rebooted if there is
no response in 60s.
3. The module cannot be rebooted frequently. When you constantly failed to restart for 3 times, you can
restart immediately for the first time after that, if it still fails, you should restart after 10 minutes for the
second time, and restart after 30 minutes for the third time, 1 hour for the fourth time, etc.
If MCU fails to transmit data to network after PPP connection has been set up, please check the
4.
configuration of PPP and the state of network, and then reboot the module.
UC20_PPP_Application_Note Confidential / Released
UMTS/HSPA Module Series
UC20 PPP Application Note
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