Specifications

TC35 / TC37 Hardware Interface Description
TC35_37_HD_02_V03.10 - Released Page 34 of 92 21.12.2001
3.3.4 Turn off GSM engine
To switch the module off the following procedures may be used:
• Normal procedure: Software controlled by sending an AT command over the RS232
application interface. See Chapter 3.3.4.1.
• Emergency shutdown: Hardware driven by switching the /PD (Power Down) line of the
ZIF connector to ground = immediate shutdown of supply voltages, only applicable if the
software controlled procedure fails! See Chapter 3.3.4.2.
• Automatic shutdown: Takes effect if undervoltage / overvoltage is detected or if battery
or board (engine) temperature exceeds critical limit. See Chapter 3.3.4.3.
3.3.4.1 Turn off GSM engine using AT command
The best and safest approach to powering down the engine is to issue the AT^SMSO
command. This procedure lets the engine log off from the network and allows the software to
enter into a secure state and to save data before disconnecting the power supply.
If the module is in Charge Only mode (not logged into the GSM network), it switches off
when the voltage is disconnected from the POWER inputs.
3.3.4.2 Emergency shutdown using /PD pin
Caution: Use the /PD pin only when, due to serious problems, the software is not
responding for more than 5 seconds. Pulling the /PD pin causes the loss of all
information stored in the volatile memory since power is cut off immediately.
Therefore, this procedure is intended only for use in case of emergency, e.g. if
TC35 fails to shut down properly.
The /PD signal is available on the ZIF connector. To control the /PD line it is recommended
to use an open drain / collector driver. To actually turn the GSM engine off, the /PD line has
to be driven to ground for ≥ 3.5 s.
Figure 10: Deactivating GSM engine by Power Down signal
How does it work:
• Voltage VBATT+ is
permanently applied to
the module.
• The module is active
while the internal reset
signal is kept at high
potential.
• The module turns of
f
once the PD signal is
grounded, the baseband
processor stops sending
watchdog pulses to the
ASIC and the VDD line
goes low.
VBATT+
Internal reset
/PD
generated by external application
max. 3.5s
generated by GSM engine
/IGT
VDD