EM77950
BB Controller
Since BB retains all the register values in power-down mode, special care should be
paid to the register values before it enters power-down. For example, the MCU should
check that the BB is not in the middle of transmitting or receiving a packet.
The RFACTIVE should be set low to shutdown the RFW-102, before entering
power-down mode.
8.2.2.2 Idle Mode
In idle mode, the BB internally blocks the clock input. The external clock is not stopped,
but it is not routed to the internal logic. By doing this, the MCU achieves substantial
power savings and yet the wake-up time is still relatively short. The power consumption
is not minimal since the external clock is still active.
All registers and FIFOs retain their values when BB is in idle mode.
BB enters idle mode by setting bit TBD in register TBD to “1”. This bit is set by the MCU
and cleared by BB.
BB goes back to working mode by setting CS_n input pin to “0” for TBD μsec.
Since BB retains all the register values in idle mode, special care should be given to the
register values before BB enters idle mode. For example, the MCU should check that
the BB is not in the middle of transmission or receiving a packet. In addition, the
RFACTIVE should be set low to shutdown the RFW-102.
8.2.3 Preamble Correlation
The transmitting BB sends the PREAMBLE in order to synchronize the receiver to its
transmission. BB transmits a fixed size PREAMBLE of 16 bits. The received
PREAMBLE has a variable length of 16Ù9 bits, determined by SCR2 [5:7]. The
receiver correlates the 16Ù9 bits from its PRE-L and PRE-H registers to the 16Ù9 bits
in its input shift-register. If a correlation was found, then BB receiver state machine is
enabled.
The purpose of the PREAMBLE is to filter the module packets from white noise or other
transmissions on the channel. NODE_ID and NET_ID filter are used to filter packets
from other module networks.
The PREAMBLE is transmitted MSB to LSB (PRE-H first and then PRE-L).
The value of the PREAMBLE is determined according to PRE-L and PRE-H registers.
The BB has the same PREAMBLE when it is in transmitting mode (TX_RX=1) as when
it is in receiving mode (TX_RX=0).
The value of the PRE-L and PRE-H registers should be identical in the BB in all nodes
in the network.
Product Specification (V1.0) 10.09.2007
(This specification is subject to change without further notice)
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ELAN [ ELAN MICROELECTRONICS CORP ]
