GSM0128IG001
30
Revision Draft – 9/22/08
6.8.3
Radio Power/Reset (Pin 22)
The Reset signal is used to force the modem to start at a known state. When the Reset is pulled low the
modem will immediately suspend any function and will not exit the reset state until the Reset signal is
released to be pulled high. Once the transition from low to high is complete, the modem will boot. The Reset
signal is falling edge triggered, so the reset function is set immediately when the signal is pulled low.
When using Reset, it will immediately detach the connection from the GSM network although this is not
considered ideal. Typically during a normal shutdown, the modem will issue a detach request to the network
to indicate that it is being removed. Reset must not be used to “power off” the device, but only as a last
resort wherein there is no response from the module.
Controlling the Reset signal must only performed by an open collector/open drain device. Driving the Reset
signal high will interfere with the normal operation of the modem power on/off sequences. Power sequencing
cannot be guaranteed if Reset is being driven high by an external device. If driving from an external
microprocessor, the reset can be controlled by driving the control pin low as an output, then change the pin
control to be an input, this will satisfy the high impedance requirement.
The Reset pin can also be monitored as a system on/off indication. When the modem is powered on during
a normal operating state, this pin will be set high. When the modem is powered down or in the “off” state,
this pin will be low. Any monitoring circuit MUST be high impedance, such as a logic gate or microprocessor
input.
Parameter
Parameter/
Conditions
MIN
TYP
MAX
UNIT
V
IL
Input Voltage – Low or
float
0.58
V
dc
V
IH
Input Voltage – High
1.36
1.95
V
dc
I
PU
Internal Pull-Up Resistor
-40
-31
-15
µA
I
IL
Reset Pulse Duration
Current Sink
10
-2.0
mA
mS
6.8.4
Using the Power Control Signal (Pin 24)
The input is equivalent to a “phone ON-button”. A failing-edge on this Active-Low input will switch ON the
module or switch OFF the module after a delay
*
. This input has a “weak pull-up” resistor internal to the
module. This input can be left grounded if the “RTC Sleep Function is not required. If RTC Sleep is required,
then the PWR_CTL line must be floated to allow the internal resistor to pull the line high.
Controlling the Power Control signal must only be performed by an open collector/open drain device. Driving
the Power Control signal high may interfere with the normal operation of the modem. If driving from an
external microprocessor, the Power Control can be controlled by driving the control pin low as an output,
then change the microprocessor’s pin control to be an input (this will satisfy the high impedance
requirement).
