AX-ConfigurationUtility User Manual
25
•
Occasionally it may be necessary to conclude the preamble with a few special
bits. This can be achieved using the field
s below “Append additional encoded
bits”.
SYNC WORD
•
In Raw Preamble Mode you can choose an arbitrary sync word of up to 32 bit as a
start of frame delimiter. However, it is recommended to use a sync word with well
peaking auto correlation function.
•
The SYNC WORD is always sent MSB first, irrespective
of the “send MSB first”
option in the DATA chunk. See comment on that option below.
•
The “unencoded” option
causes the SYNC WORD to bypass the manchester,
scrambler, differential and inversion encoder
3
.
Correspondingly the RX matching unit detecting the SYNC WORD will operate on
the bit stream before decoding.
•
DC content, running DC content and the number of transitions is computed in
order to indicate the quality of the selected SYNC WORD. Large DC or running DC
components can impede correct frequency tracking, whereas a low number of
transitions slows down time tracking.
•
Selecting the “enable SFD callback” option causes the AXRadioAPI to notify the
application level firmware each time a start of frame delimiter (a SYNC WORD or
a HDLC flag) has been received.
LEN & MAC
•
“MAC header length” specifies the length of the packet header, which can contain
a length field, a sequence number for acknowledge and addresses.
•
In Raw Pattern Match mode, a length field can be used to communicate the length
of the current packet to the RX. Alternatively (uncheck “enable len
field
”) the RX
can be configured to expect packets of a fixed length.
•
“
Position [Bits]
” determines
the position of the length field inside the packet
header. Zero means the length field follows immediately after the SYNC word.
•
“Significant bits” tells
the RX how many bits of the length field are used to encode
the packet length. This is useful if your protocol uses a shared byte to encode the
packet length plus something else.
•
“len offset”: The actual packet length (excluding SYNC WORD & CRC) assumed by
the RX is len + len offset. E.g. set len offset to zero if in your protocol the length
byte counts the number of bytes including the length byte. Set len offset = 1 if
3
Bypassing the encoder is achieved by setting the UNENC flag corresponding FIFO DATA chunk. This causes the
chunk data to bypass manchester, scrambler and differential encoder, however inversion still applies. For
convenience AX-ConfigurationUtility therefore inverts preamble and SYNC WORD bytes before writing them to
the firmware code if “unencoded” and INV encoding are selected.
