AC75 Hardware Interface Description
Strictly confidential / Preliminary
s
AC75_HD_V00.202
Page 47 of 120
27.04.2006
3.6 Power
Saving
Intended for power saving, SLEEP mode reduces the functionality of the AC75 to a minimum
and thus minimizes the current consumption. Settings can be made using the AT+CFUN
command. For details see [1]. SLEEP mode falls in two categories:
•
NON-CYCLIC SLEEP mode: AT+CFUN = 0
•
CYCLIC SLEEP modes, AT+CFUN = 7 or 9.
The functionality level AT+CFUN=1 is where power saving is switched off. This is the default
after startup.
NON-CYCLIC SLEEP mode permanently blocks the serial interface. The benefit of the
CYCLIC SLEEP mode is that the serial interface remains accessible and that, in intermittent
wake-up periods, characters can be sent or received without terminating the selected mode.
This allows the AC75 to wake up for the duration of an event and, afterwards, to resume
power saving. Please refer to [1] for a summary of all SLEEP modes and the different ways
of waking up the module.
For CYCLIC SLEEP mode both the AC75 and the application must be configured to use
hardware flow control. This is necessary since the CTSx signal is set/reset every 0.9-2.7
seconds in order to indicate to the application when the UART is active. Please refer to [1] for
details on how to configure hardware flow control for the AC75.
Note: Although not explicitly stated, all explanations given in this section refer equally to
ASC0 and ASC1, and accordingly to CTS0 and CTS1 or RTS0 and RTS1.
3.6.1 Network Dependency of SLEEP Modes
The power saving possibilities of SLEEP modes depend on the network the module is
registered in. The paging timing cycle varies with the base station. The duration of a paging
interval can be calculated from the following formula:
t = 4.615 ms (TDMA frame duration) * 51 (number of frames) * DRX value
.
DRX (Discontinuous Reception) is a value from 2 to 9, resulting in paging intervals from
0.47-2.12 seconds. The DRX value of the base station is assigned by the network operator.
In the pauses between listening to paging messages, the module resumes power saving, as
shown in Figure 10.
Figure 10: Power saving and paging
The varying pauses explain the different potential for power saving. The longer the pause the
less power is consumed.
0.47-2.12 s
0.47-2.12 s
0.47-2.12 s
Paging
Paging
Paging
Paging
Power Saving
Power Saving
Power Saving
