CC110L Datasheet, PDF (33/85 Pages) Texas Instruments – Value Line Transceiver

15.2.3 CRC Filtering
The filtering of a packet when CRC check fails
is
enabled
by
setting
PKTCTRL1.CRC_AUTOFLUSH=1. The CRC
auto flush function will flush the entire RX
FIFO if the CRC check fails. After auto flushing
the RX FIFO, the next state depends on the
MCSM1.RXOFF_MODE setting.
When using the auto flush function, the
maximum packet length is 63 bytes in variable
packet length mode and 64 bytes in fixed
15.3 Packet Handling in Transmit Mode
The payload that is to be transmitted must be
written into the TX FIFO. The first byte written
must be the length byte when variable packet
length is enabled. The length byte has a value
equal to the payload of the packet (including
the optional address byte). If address
recognition is enabled on the receiver, the
second byte written to the TX FIFO must be
the address byte.
If fixed packet length is enabled, the first byte
written to the TX FIFO should be the address
(assuming the receiver uses address
recognition).
The modulator will first send the programmed
number of preamble bytes. If data is available
15.4 Packet Handling in Receive Mode
In receive mode, the demodulator and packet
handler will search for a valid preamble and
the sync word. When found, the demodulator
has obtained both bit and byte synchronization
and will receive the first payload byte.
When variable packet length mode is enabled,
the first byte is the length byte. The packet
handler stores this value as the packet length
and receives the number of bytes indicated by
the length byte. If fixed packet length mode is
used, the packet handler will accept the
programmed number of bytes.
15.5 Packet Handling in Firmware
When implementing a packet oriented radio
protocol in firmware, the MCU needs to know
when a packet has been received/transmitted.
Additionally, for packets longer than 64 bytes,
the RX FIFO needs to be read while in RX and
the TX FIFO needs to be refilled while in TX.
This means that the MCU needs to know the
number of bytes that can be read from or
written to the RX FIFO and TX FIFO
respectively. There are two possible solutions
to get the necessary status information:
CC110L
packet length mode. Note that when
PKTCTRL1.APPEND_STATUS is enabled, the
maximum allowed packet length is reduced by
two bytes in order to make room in the RX
FIFO for the two status bytes appended at the
end of the packet. Since the entire RX FIFO is
flushed when the CRC check fails, the
previously received packet must be read out of
the FIFO before receiving the current packet.
The MCU must not read from the current
packet until the CRC has been checked as
OK.
in the TX FIFO, the modulator will send the
two-byte (optionally 4-byte) sync word followed
by the payload in the TX FIFO. If CRC is
enabled, the checksum is calculated over all
the data pulled from the TX FIFO, and the
result is sent as two extra bytes following the
payload data. If the TX FIFO runs empty
before the complete packet has been
transmitted, the radio will enter
TXFIFO_UNDERFLOW state. The only way to
exit this state is by issuing an SFTX strobe.
Writing to the TX FIFO after it has underflowed
will not restart TX mode.
Next, the packet handler optionally checks the
address and only continues the reception if the
address matches. If automatic CRC check is
enabled, the packet handler computes CRC
and matches it with the appended CRC
checksum.
At the end of the payload, the packet handler
will optionally write two extra packet status
bytes (see Table 23 and Table 24) that contain
CRC status, link quality indication, and RSSI
value.
a) Interrupt Driven Solution
The GDO pins can be used in both RX and TX
to give an interrupt when a sync word has
been received/transmitted or when a complete
packet has been received/transmitted by
setting IOCFGx.GDOx_CFG=0x06. In addition,
there are two configurations for the
IOCFGx.GDOx_CFG register that can be used
as an interrupt source to provide information
on how many bytes that are in the RX FIFO
and TX FIFO respectively. The
SWRS109A
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