CC2550RSTR Datasheet, PDF (21/61 Pages) Texas Instruments – Low-Cost Low-Power 2.4 GHz RF Transmitter

CC2550
sync word and then the data bytes. The
number of preamble bytes is programmed with
the MDMCFG1.NUM_PREAMBLE value.
The synchronization word is a two-byte value
set in the SYNC1 and SYNC0 registers. A one-
byte sync word can be emulated by setting the
SYNC1 value to the preamble pattern. It is also
possible to emulate a 32 bit sync word by
using MDMCFG2.SYNC_MODE=3 or 7. The sync
word will then be repeated twice.
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. As
described in the next section, this can be used
to support packet formats with different length
configuration than natively supported by
CC2550. One should make sure that TX mode
is not turned off during the transmission of the
first half of any byte. Refer to the CC2550
Errata Notes [1] for more details.
Note that the minimum packet length
supported (excluding the optional length byte
and CRC) is one byte of payload data.
13.2.1 Packet Length > 255
Reprogramming the packet automation control
register, PCKCTRL0, during TX mode opens
the possibility to transmit packets that are
longer than 256 bytes and still be able to use
the packet handling hardware support. At the
start of the packet, the infinite packet length
mode (PCKCTRL0.LENGTH_CONFIG=2) must
be active. The PKTLEN register is set to
mod(length, 256). When less than 256 bytes
remains of the packet the MCU disables
infinite packet length mode and activates fixed
packet length mode. When the internal byte
counter reaches the PKTLEN value, the
transmission ends the radio enters the state
determined by TXOFF_MODE). Automatic CRC
appending can be used (by setting
PKTCTRL0.CRC_EN=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.
• Pre-program the PKTLEN register to
mod(600,256)=88.
• Transmit at least 345 bytes (600 – 255),
for example by filling the 64-byte TX FIFO
six times (384 bytes transmitted).
• Set PKTCTRL0.LENGTH_CONFIG=0.
• The transmission ends when the packet
counter reaches 88. A total of 600 bytes
are transmitted.
Figure 11: Packet Length > 255
SWRS039B
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