User's Manual

MC55/56 Hardware Interface Description
Confidential / Preliminary
s
MC55/56_hd_v03.00 Page 32 of 104 16.08.2005
3.3.2 Turn off MC55/56
To switch the module off the following procedures may be used:
• Normal shutdown procedure: Software controlled by sending the AT^SMSO command
over the serial application interface. See Chapter 3.3.2.1.
• Emergency shutdown: Hardware driven by switching the /EMERGOFF line of the board-
to-board-connector to ground = immediate shutdown of supply voltages, only applicable
if the software controlled procedure fails! See Chapter 3.3.2.2.
• Automatic shutdown: See Chapter 3.3.3
a) Takes effect if undervoltage is detected.
b) Takes effect if MC55/56 board temperature exceeds critical limit.
3.3.2.1 Turn off MC55/56 using AT command
The best and safest approach to powering down MC55/56 is to issue the AT^SMSO
command. This procedure lets MC55/56 log off from the network and allows the software to
enter into a secure state and safe data before disconnecting the power supply. The mode is
referred to as POWER DOWN mode. In this mode, only the RTC stays active.
Before switching off the device sends the following response:
^SMSO: MS OFF
OK
^SHUTDOWN
After sending AT^SMSO do not enter any other AT commands. There are two ways to verify
when the module turns off:
• Wait for the URC “^SHUTDOWN”. It indicates that data have been stored non-volatile
and the module turns off in less than 1 second.
• Also, you can monitor the VDD pin. The low state of VDD definitely indicates that the
module is switched off.
Be sure not to disconnect the operating voltage V
BATT+
before the URC “^SHUTDOWN” has
been issued and the VDD signal has gone low. Otherwise you run the risk of losing data.
While MC55/56 is in POWER DOWN mode the application interface is switched off and must
not be fed from any other source. Therefore, your application must be designed to avoid any
current flow into any digital pins of the application interface.
Note: In POWER DOWN mode, the /EMERGOFF pin, the output pins of the ASC0 interface
/RXD0, /CTS0, /DCD0, /DSR0, /RING0 and the output pins of the ASC1 interface
/RXD1 and /CTS1 are switched to high impedance state.
If this causes the associated input pins of your application to float, you are advised to
integrate an additional resistor (100 k – 1 M) at each line. In the case of the
/EMERGOFF pin use a pull-down resistor tied to GND. In the case of the serial
interface pins you can either connect pull-up resistors to the VDD line, or pull-down
resistors to GND.