RM0453 Rev 2 167/1454
RM0453 Sub-GHz radio (SUBGHZ)
217
Variable length generic packet mode
When the packet is of uncertain or variable length, the information on the payload length
must be transmitted within the packet. For this, a header with the payload length information
is transmitted after the syncword.
Fixed length generic packet mode
In certain operation modes where the payload length is fixed or known in advance, it may be
advantageous to reduce transmission time by invoking fixed length generic packet mode. In
this mode, the header is not present in the packet frame and the payload length must be
configured on both sides of the sub-GHz radio link.
Node or broadcast address
The node or broadcast address are not considered part of the payload. They are added
automatically when enabled by Set_PacketParams() command. Adding these fields
allows the user to perform additional packet filtering at the header level.
Whitening
Whitening is based on a 9-bit LFSR and used to whiten the payload and, when present, the
header and CRC. Whitening limits a sequence of consecutive 1 or 0 bit to nine. The
whitening polynomial is x
9
+ x
5
+ 1, and can be initialized with the whitening initial value in
WHITEINI[8:0].
CRC
CRC computation can be configured for polynomial and initial value, and allows inversion.
Configuration is done through Set_PacketParams() command.
The flexible CRC configuration allows any standard CRC or proprietary CRC to be
generated and checked, for example:
• IBM CRC configuration
– CRC polynomial 0x8005
– CRC initial value 0xFFFF
– 2-byte length CRC
• CCIT CRC configuration
– CRC polynomial 0x1021
– CRC initial value 0x1D0F
– 2-byte length inverted CRC
5.5.6 BPSK modem
The BPSK modem provides a BPSK modulation for data rates of 100 and 600 bit/s. BPSK
modulation is only available in transmit mode. The modulation offers a raise-cosine pulse
shape filter with a BT of 0.5. The BPSK modulator can be changed into DBPSK modulation
by some host pre-processing on the data to be transmitted.
All modulation parameters are set by Set_ModulationParams() command.
The bit rate (or equivalent chip) is controlled by Br parameter, defined as follows:
Br = HSE32
FREQ
/ BitRate where HSE32
FREQ
= 32 MHz.
To Next Page
Loading...
Need help?
General
