CC1101
SWRS061H Page 39 of 98
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. This value must be different from 0.
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 CRC. The PKTLEN register is
used to set the maximum packet length
allowed in RX. Any packet received with a
length byte with a value greater than PKTLEN
will be discarded. The PKTLEN value must be
different from 0.The first byte written to the
TXFIFO must be different from 0.
With PKTCTRL0.LENGTH_CONFIG=2, the
packet length is set to infinite and transmission
and reception 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
CC1101
. One should make sure
that TX mode is not turned off during the
transmission of the first half of any byte. Refer
to the
CC1101
Errata Notes [3] for more details.
15.2.1 Arbitrary Length Field Configuration
The packet length register, PKTLEN, can be
reprogrammed during receive and transmit. In
combination with fixed packet length mode
(PKTCTRL0.LENGTH_CONFIG=0), this opens
the possibility to have a different length field
configuration than supported for variable
length packets (in variable packet length mode
the length byte is the first byte after the sync
word). At the start of reception, the packet
length is set to a large value. The MCU reads
out enough bytes to interpret the length field in
the packet. Then the PKTLEN value is set
according to this value. The end of packet will
occur when the byte counter in the packet
handler is equal to the PKTLEN register. Thus,
the MCU must be able to program the correct
length, before the internal counter reaches the
packet length.
15.2.2 Packet Length > 255
The packet automation control register,
PKTCTRL0, can be reprogrammed during TX
and RX. This opens the possibility to transmit
and receive 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
(PKTCTRL0.LENGTH_CONFIG=2) must be
active. On the TX side, the PKTLEN register is
set to mod(length, 256). On the RX side the
MCU reads out enough bytes to interpret the
length field in the packet and sets the PKTLEN
register 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 or reception ends (the
radio enters the state determined by
TXOFF_MODE or RXOFF_MODE). Automatic
CRC appending/checking can also 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 20)
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.
Note: The minimum packet length
supported (excluding the optional length
byte and CRC) is one byte of payload
data.
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