CC112X/CC1175
SWRU295C
Page 43 of 108
The preamble pattern is an alternating se
quence of ones and zeros (1010∙∙/0101∙∙/
00110011
∙∙/11001100∙∙) programmable through the
field.
The
minimum
length
of
the
preamble
is
programmable
through
the
register field. When strobing TX, the modulator will start
transmitting a preamble. When the programmed number of preamble bytes has been transmitted, the
modulator will send the sync word and then data from the TX FIFO. If the TX FIFO is empty, the
modulator will continue to send preamble bytes until the first byte is written to the TX FIFO. The
modulator will then send the sync word and then the data bytes.
registers. The sync word provides byte synchronization of
the incoming packet. Non-supported sync word lengths can be emulated by using parts of the
preamble pattern in the
registers.
CC112X
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. The packet length is defined as the payload data and the optional address
byte, excluding the optional length byte, the optional CRC, and the optional append status.
7.1.1
Fixed Packet Length
Fixed packet length mode is selected by setting
. The desired
packet length is set by the
register.
To support non-byte oriented protocols, fixed packet length mode supports packet lengths of n bytes
+ m bits, where n is programmed through the
register and m is programmed through
If m ≠ 0, only m bits of the last byte written to the TX FIFO is transmitted
and RX mode is terminated when the last m bits of the packet is received. This is very useful in low
power systems where it is important not to stay in TX/RX longer than necessary. CRC is not
supported when
.
In RX, you will read zero‟s from the (8 − m) LSBs in
the last byte in the RX FIFO.
PKT_LEN = 0x00
PKT_CFG0.PKT_BIT_LEN ≠ 000
the packet length is between 1
and 7 bits long (given by the
register field). If
PKT_LEN = 0x00
and
PKT_CFG0.PKT_BIT_LEN = 000
the packet length is 256 bytes.
7.1.2
Variable Packet Length
In variable packet length mode,
,
the packet length is configured
by the first byte after the sync word. The packet length is defined as the payload data and optional
address field, excluding the length byte and the optional CRC. The
register is used to set
the maximum packet length allowed in RX. Any packet received with a length byte with a value
greater than
will be discarded.
PKT_CFG0.LENGTH_CONFIG = 11b
only the 5 LSB of the length byte is used for length
configuration while the 3 MSB are treated as normal data. Maximum packet length is hence 32 bytes.
The only difference from standard variable length mode is the masking of 3 MSB bits of the received
packet length byte, configured through
7.1.3
Infinite Packet Length
With
PKT_CFG0.LENGTH_CONFIG = 10b
, 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
CC112X
.
Note:
The minimum packet length supported (excluding the optional length byte and CRC) is
one byte of payload data.