Neo_M660A GPRS Module Hardware User Guide
Copyright © Neoway Technology Co., Ltd
15
Figure 3-10
Reference circuit for power-on controlled by high level
USER_ON
GPRS Module
ON/OFF
4.7K
47K
R1
R2
In Figure 3-10, high level takes effect for
ON/OFF
on the user side (USER_ON). R1 and R2 can be adjusted
according to the driving capability of the USER_ON pin. Use a common NPN transistor, e.g. MMBT3904;
or a digital NPN transistor, e.g. DTC123. If digital transistor is used, delete R1 and R2.
Level abnormalities at interfaces connected to the external MCU, especially the UART port, might
affect the power on procedure of the module. For example, when a module is turned on, the IO ports of
the MCU are still in output status because they have not been initialized completely. The module
might fails to start if the UTXD signal (output pin) is forced to pull up or down.
The better way to rescue the module from abnormal condition, is to apply a power OFF-ON procedure,
rather than using the ON/OFF control signal. In fact ON/OFF signal is software-dependent.
3.1.5 RESET
Pull the RESET signal to low level for more than 100 ms to reset the module. A pull-up resistor is internally
included and the typical high level is 2.8 V. The RESET pin can be left disconnected if not used. A triode
has been used in the internal RESET circuit. Please refer to Figure 3-11.
Figure 3-11
Reset circuit with triode separating
Reset
Circuit
R1
R2
2
.8
V
RESET
GPRS Module
