BR-EVAL2.0 BlueRadios Inc, BR-EVAL2.0 Datasheet - Page 59

• Manufacturer Part Number: BR-EVAL2.0
• Description: EVAL KIT BLUETOOTH VER2.0
• Manufacturer: BlueRadios Inc
• Type: Bluetooth V 2.0r

Specifications of BR-EVAL2.0

• Frequency: 2.4GHz
• For Use With/related Products: Bluetooth
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: 822-1001

Bluetooth connections are master/slave in nature. A master sends packets and a slave has to acknowledge
that packet in the next timeslot. Timeslots in Bluetooth are 625 microseconds wide. This implies that a
master will always know when packets will be sent and received, which further means it is able to optimize
power usage by switching on power hungry circuitry only when needed.
A slave on the other hand does NOT have prior knowledge of when a packet will be received and has to
assume that a packet will be received from a master on every receive slot. This means that it has to leave it’s
receiving circuitry on for most of the receive slot duration. The result of this is high power consumption where
a slave with no data transmission still consumes around 5mA.
This problem was identified very early in the evolution of Bluetooth (especially since headsets spend all their
time as a slave in a Bluetooth connection) and it was solved by having a mode called Sniff, with appropriate
lower layer negotiating protocol.
Sniff mode during connection is basically an agreement between the slave and its master of which data packets
will only be exchanged for N timeslots every M slots. The slave can then assume that it will never be contacted
during N-M slots, and so can switch its power hungry circuitry off. The specification goes further by also
specifying a third parameter called ‘timeout’ (T) which specifies ‘extra’ timeslots that the slave will agree to listen
for after receiving a valid data packet. Put another way, if a data packet is received by the slave, then it knows
that it MUST carry on listening for at least T more slots. If within that T slot time period another data packet is
received, then the timer is restarted. This mechanism ensures low power consumption when there is no data
transfer – at the expense of latency. When there is a lot of data to be transferred, it acts as if sniff mode were
not enabled.
It is stated above that during sniff mode, a slave listens for N slots every M slots. The Bluetooth specification
states that a master can have up to 7 slaves attached to it with all slaves having requested varying sniff
parameters. It may therefore be impossible to guarantee that each slave gets the M parameter it requested. In
Low Pow er Modes Using Sniff
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 if
data is sent infrequently. However if data is constantly transmitted there is no power saving benefit to use Sniff.
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.
Park Suppoted in Point-to-Point mode only!
3.7.3
7173 S. Havana Street, Suite 600
Sniff and Park (Connected Slave)
EXAMPLE:
TYPE :
REPLY:
ATCPAIR<cr>
<cr_lf>OK<cr_lf>
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BlueRadios, Inc.
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