CC1101
SWRS061H Page 40 of 98
0,1,..........,88,....................255,0,........,88,..................,255,0,........,88,..................,255,0,.......................
Internal byte counter in packet handler counts from 0 to 255 and then starts at 0 again
Length field transmitted and received. Rx and Tx PKTLEN value set to mod(600,256) = 88
Infinite packet length enabled
Fixed packet length
enabled when less than
256 bytes remains of
packet
600 bytes transmitted and
received
Figure 20: Packet Length > 255
15.3 Packet Filtering in Receive Mode
CC1101
supports three different types of
packet-filtering; address filtering, maximum
length filtering, and CRC filtering.
15.3.1 Address Filtering
Setting PKTCTRL1.ADR_CHK to any other
value than zero enables the packet address
filter. The packet handler engine will compare
the destination address byte in the packet with
the programmed node address in the ADDR
register and the 0x00 broadcast address when
PKTCTRL1.ADR_CHK=10 or both the 0x00
and 0xFF broadcast addresses when
PKTCTRL1.ADR_CHK=11. If the received
address matches a valid address, the packet
is received and written into the RX FIFO. If the
address match fails, the packet is discarded
and receive mode restarted (regardless of the
MCSM1.RXOFF_MODE setting).
If the received address matches a valid
address when using infinite packet length
mode and address filtering is enabled, 0xFF
will be written into the RX FIFO followed by the
address byte and then the payload data.
15.3.2 Maximum Length Filtering
In variable packet length mode,
PKTCTRL0.LENGTH_CONFIG=1, the
PKTLEN.PACKET_LENGTH register value is
used to set the maximum allowed packet
length. If the received length byte has a larger
value than this, the packet is discarded and
receive mode restarted (regardless of the
MCSM1.RXOFF_MODE setting).
15.3.3 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
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.
15.4 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).
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