User guide

RN Commands Version 4.25, 11/1/2007 Page 14 of 25
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Examples:
S*,0101 GPIO-8 driven HIGH.
S*,0100 GPIO-8 driven LOW.
S*,0202 GPIO-9 driven HIGH.
4. 1 Using Low Power Modes
4.1.1 Inquiry(Discovery) and Page(Connection) Windows
There are 2 timers that can be used to lower the idle Slave mode power of the radio. When not connected, the
Radio is active for a percentage of time listening to see if any other device wants to Discovery (inquire) or
Connect (page). The amount of time the radio is on is called the window, and the rate at which the process cycles
is called the interval. The interval is fixed at 0x800 (1.28seconds) with Sniff disabled, and 2.56 seconds with Sniff
enabled. The window can be adjusted. The default window is 0x200 (320 ms) or 25% duty cycle.
By lowering the window value, power can be saved at the expense of possibly missing an inquiry or page. Since
the host usually retries automatically many times, the only downside is a delay in discovery or connection time.
The minimum window for inquiry or page is 0x0012 (11.25ms). corresponding to about a 1% duty cycle.
Thus, average power can be reduced from >20ma to <5ma in standard mode, and <3ma in Sniff mode.
It is also possible (and desirable for security reasons) to completely disable inquiry. Once a host has found and
installed a device, inquiry is not needed, only page is used to make a connection.
To disable inquiry and still allow connections, set the Inquiry timer to 0 with “SI,0000”.
4.1.2 SNIFF mode
Sniff mode is another power conservation method utilized by Bluetooth. By default, Sniff mode is disabled, and
the radio is active continuously when connected (about 25-30ma) . In Sniff mode, the radio wakes up at specific
intervals, and sleeps in very low power mode (around 2ma) otherwise. The power savings can be quite dramatic.
To enable it, use the “SW,<hex word>“ command.
Example interval timers:
0x0020 = 20ms. (32 decimal * .625 = 20).
0x0050 = 50ms, 0x00A0 = 100ms, 0x0190 = ¼ second, 0x0320 = ½ second, 0x0640 = 1 second.
Sniff mode only pertains to an active connection. When a connection is made, both master and slave must
support Sniff mode, and agree to the Sniff window, otherwise the radio will stay in full active on mode.
Note: the maximum allowed Sniff interval is about 20 seconds = 0x7FFF sniff word setting.
Enabling DEEP SLEEP.