UMTS/HSPA Module Series
UC20 PPP Application Note
UC20_PPP_Application_Note Confidential / Released 11 / 29
4 UART/USB for PPP Connection
4.1. Data Mode and Command Mode
Module communicates information with application by UART/USB port, including AT commands and data.
There are two modes for module’s port. One is data mode and the other is command mode. Module’s port
is in command mode before PPP setup, and module can execute AT commands in this state. When PPP
negotiating is started, module’s port will enter into data mode. Module will be kept in data mode when PPP
connection was set up and module cannot execute AT commands in data mode. Quectel standard
modules provide convenient methods to switch between the modes.
4.1.1. Switch from Data Mode to Command Mode
4.1.1.1. Use DTR Level Switch from Data Mode to Command Mode
When PPP connection already exists and module is in data mode, you can change module from data
mode to command mode by setting command of AT&D1 and switching DTR level from low to high. If
module’s mode is changed successfully in this way, module will return “OK”.
4.1.1.2. Use Sequence +++ to Switch from Data Mode to Command Mode
Another way to switch module from data mode to command mode is using sequence +++ when PPP
connection has been set up successfully. To prevent the +++ escape sequence from being misinterpreted
as data, it should comply with the following sequences:
Do not input any character within 1s or longer,
Input “+++” within 1s, and no other characters can be inputted during this time,
Do not input any character within 1s after “+++” has been inputted.
When such particular sequence +++ is received, module will switch from data mode to command mode
and return “OK” for this kind of operation.
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