CC2550_06 Datasheet, PDF (20/55 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transmitter

CC2550
CC2550 supports both fixed packet length
protocols and variable packet length protocols.
Variable or fixed packet length mode can be
used for packets up to 255 bytes. For longer
packets, infinite packet length mode must be
used.
Fixed packet length mode is selected by
setting PKTCTRL0.LENGTH_CONFIG=0. The
desired packet length is set by the PKTLEN
register.
In variable packet length mode,
PKTCTRL0.LENGTH_CONFIG=1, the packet
length is configured by the first byte after the
sync word. The packet length is defined as the
payload data, excluding the length byte and
the optional automatic CRC.
With PKTCTRL0.LENGTH_CONFIG=2, the
packet length is set to infinite and transmission
will continue until turned off manually. The
infinite mode can be turned off while a packet
is being transmitted. As described in the next
section, this can be used to support packet
formats with different length configuration than
natively supported by CC2550.
13.2.1 Arbitrary length field configuration
By utilizing the infinite packet length option,
arbitrary packet length is available. At the start
of the packet, the infinite mode must be active.
On the TX side, the PKTLEN register is set to
mod(length, 256). When less than 256
bytes remains of the packet the MCU disables
infinite packet length and activates fixed length
packets. When the internal byte counter
reaches the PKTLEN value, the transmission
ends. Automatic CRC appending/checking can
be used (by setting PKTCTRL0.CRC_EN to 1).
When for example a 600-byte packet is to be
transmitted, the MCU should do the following
(see also Figure 11):
• Set PKTCTRL0.LENGTH_CONFIG=2 (10).
• Pre-program the PKTLEN register to
mod(600,256)=88.
• Transmit at least 345 bytes, for example
by filling the 64-byte TX FIFO six times
(384 bytes transmitted).
• Set PKTCTRL0.LENGTH_CONFIG=0 (00).
• The transmission ends when the packet
counter reaches 88. A total of 600 bytes
are transmitted.
Figure 11: Arbitrary length field configuration
PRELIMINARY Data Sheet (Rev.1.2) SWRS039A
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