CC2500_06 Datasheet, PDF (26/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

CC2500
15 Packet Handling Hardware Support
The CC2500 has built-in hardware support for
packet oriented radio protocols.
In transmit mode, the packet handler will add
the following elements to the packet stored in
the TX FIFO:
• A programmable number of preamble
bytes.
• A two byte synchronization (sync) word.
Can be duplicated to give a 4-byte sync
word.
• Optionally whiten the data with a PN9
sequence.
• Optionally Interleave and Forward Error
Code the data.
• Optionally compute and add a CRC
checksum over the data field.
• The recommended setting is 4-byte
preamble and 4-byte sync word except for
500 kbps data rate where the
recommended preamble length is 8 bytes.
In receive mode, the packet handling support
will de-construct the data packet:
• Preamble detection.
• Sync word detection.
• Optional one byte address check.
• Optionally compute and check CRC.
• Optionally append two status bytes (see
Table 21 and Table 22) with RSSI value,
Link Quality Indication and CRC status.
Bit Field name Description
7:0 RSSI
RSSI value
Table 21: Received packet status byte 1
(first byte appended after the data)
Bit Field name Description
7
CRC_OK
1: CRC for received data OK (or
CRC disabled)
0: CRC error in received data
6:0 LQI
The Link Quality Indicator
estimates how easily a received
signal can be demodulated
Table 22: Received packet status byte 2
(second byte appended after the data)
Note that register fields that control the packet
handling features should only be altered when
CC2500 is in the IDLE state.
15.1 Data Whitening
From a radio perspective, the ideal over the air
data are random and DC free. This results in
the smoothest power distribution over the
occupied bandwidth. This also gives the
regulation loops in the receiver uniform
operation conditions (no data dependencies).
Real world data often contain long sequences
of zeros and ones. Performance can then be
improved by whitening the data before
transmitting, and de-whitening in the receiver.
With CC2500, this can be done automatically
by setting PKTCTRL0.WHITE_DATA=1. All
data, except the preamble and the sync word,
are then XOR-ed with a 9-bit pseudo-random
(PN9) sequence before being transmitted as
shown in Figure 10. At the receiver end, the
data are XOR-ed with the same pseudo-
random sequence. This way, the whitening is
reversed, and the original data appear in the
receiver.
Data whitening can only be used when
PKTCTRL0.CC2400_EN = 0 (default).
PRELIMINARY Data Sheet (Rev.1.2) SWRS040A
Page 26 of 83