User's Manual

XT55/56 Hardware Interface Description
Confidential / Released
s
XT55/56_hd_v02.06a Page 48 of 125 17.12.2004
3.6 Power saving
SLEEP mode reduces the functionality of the GSM part of the XT55/56 module to a minimum
and, thus, minimizes the current consumption to the lowest level. Settings can be made
using the AT+CFUN command. For details see below and [1]. SLEEP mode falls into two
categories:
• NON-CYCLIC SLEEP mode AT+CFUN=0
• CYCLIC SLEEP modes, selectable with AT+CFUN=5, 6, 7, 8 or 9.
IMPORTANT: Please keep in mind that power saving works properly only when PIN
authentication has been done. If you attempt to activate power saving while the SIM card is
not inserted or the PIN not correctly entered (Limited Service), the selected <fun> level will
be set, though power saving does not take effect. For the same reason, power saving cannot
be used if the GSM part of the XT55/56 operates in Alarm mode.
To check whether power saving is on, you can query the status of AT+CFUN if you have
chosen CYCLIC SLEEP mode. If available, you can take advantage of the status LED
controlled by the GSM_SYNC pin (see Chapter 3.12.2.2). The LED is off in all SLEEP modes
when no activity occurs, but resumes flashing to indicate temporary wake-up states during
CYLCIC SLEEP modes. The LED patterns are shown in Table 18.
The wake-up procedures are quite different depending on the selected SLEEP mode. Table
11 compares the wake-up events that can occur in NON-CYCLIC and CYCLIC SLEEP
modes.
3.6.1 No power saving (AT+CFUN=1)
The functionality level <fun>=1 is where power saving is switched off. This is the default after
startup.
3.6.2 NON-CYCLIC SLEEP mode (AT+CFUN=0)
If level 0 has been selected (AT+CFUN=0), the serial interface is blocked. The module
shortly deactivates power saving to listen to a paging message sent from the base station
and then immediately resumes power saving. Level 0 is called NON-CYCLIC SLEEP mode,
since the serial interface is not alternatingly made accessible as in CYCLIC SLEEP mode.
The first wake-up event fully activates the module, enables the serial interface and
terminates the power saving mode. In short, it takes the GSM part of the XT55/56 back to the
highest level of functionality <fun>=1. GSM_RTS0 or GSM_RTS1 are not used for flow
control, but to wake up the module.
3.6.3 CYCLIC SLEEP mode (AT+CFUN=5, 6, 7, 8)
The major benefit over the NON-CYCLIC SLEEP mode is that the serial interface is not
permanently blocked and that packet switched calls may go on without terminating the
selected CYCLIC SLEEP mode. This allows the GSM part of the XT55/56 to become active,
for example to perform a GPRS data transfer, and to resume power saving after the GPRS
data transfer is completed.