Uart Interface - Zte MG2639 User Manual

 Power off
To turn off the module, use AT command "AT+ZPWROFF" or provide a 2s~5s low level pulse to
PWRKEY_N PIN.
 Reset
Use the above method to firstly "power-off" and then "power-on" to hard reset the module.
If the external reset function has to be used, low level pulse lasting at least 500ms should be
provided to /RESET Pin within 2 seconds after the module is turned on. Before that, the external
I/O signal must be kept at low level. See the reset circuit design in figure 4-1.
If SYSRST_N Pin is not used, suspend the pin.
See the module's power-on/off time sequence in the diagram below:
t
a
20ms
 V_MSM
There is a voltage output pin with current adjuster, which can be used to supply external power to
the board. The voltage of this pin and the voltage of baseband processor/memory come from the
same voltage adjuster. The voltage output is available only when the module is on. The normal
output voltage is 2.85V, and the user should absorb the current from this pin as little as possible
(less than 10mA). Generally, it is recommended to use this pin to match the level.
When the module is off, the output voltage for this pin remains unchanged, but the impedance is
rather high. Therefore, it's not recommended to use this pin for other purposes.
 Other advice
In order to make sure the data is saved safely, please don't cut off the power when the module is
on. It's strongly recommended to add battery or soft switch like the power key on the module.

4.2 UART interface

Note: when using the module for overall design, the users should export UART for module's
software upgrade.
MG2639 module provides an integrated full duplex UART interface and an accessorial full duplex
UART interface, whose maximal data rate is 115200bps. External interface is 2.8VCMOS level
signal, their logic functions conform to RS-232 interface standard. These two UART could be used
as serial port data interfaces, usually UART1 is used for AT commands, data transmission and
updating software of module.
The module's output IO level is 2.8V，it needs to transfer the level when connecting with standard
3.3V or 5V logic circuit（such as MCU or RS232 drive chip MAX3238 etc）, Figure 4-3 shows the
COM port level transfer circuit. The converted signal should connect with MCU or RS232 drive chip
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Figure 4-1 Power-on/off time sequence
Table 4-2 Power-on/off circuit time characteristics
t
b
10ms
t t
c d
3s 3s
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transmit without ZTE
Corporation's permission.
t
e
6s