DW1000 User Manual
© Decawave Ltd 2017
Version 2.12
Page 150 of 242
In cases where a response is expected at a particular time, this timeout can be used to flag that the expected
response is not starting on time and hence to turn off the receiver earlier than would otherwise be the case,
(i.e. if just employing the frame wait timeout). This can give a good power saving, in situations of sending a
message and awaiting a response that often does not come.
The DRX_PRETOC is programmed in units of PAC size, which can be 8, 16, 32 or 64 symbols. Table 60 gives
the preamble symbol lengths. The PAC size is set in
Sub-Register 0x27:08 – DRX_TUNE2
. As this is a 16-bit
counter the maximum preamble detection timeout possible is 65535 × (
PAC size)
, a period of over 500 ms
for the smallest PAC size. A value of zero disables the preamble detection timeout.
Example: Supposing our preamble length is 1024 symbols and the PAC size is set to 32 (in line with Table 6)
and, we send a message and know that the response (if present) will come after exactly 30 ms (because the
responder is using delayed send to begin the response exactly 30 ms after receiving our message). We can
command a 30 ms delayed receive (timed from our message transmission time) and have DRX_PRETOC
programmed to a value of 32, which is the preamble length (1024) divided by the PAC size (32).
Note that the counter automatically adds 1 to the programmed value so DRX_PRETOC should be
programmed to be 1 less than the desired value.
7.2.40.10
Sub-Register 0x27:26
– DRX_TUNE4H
ID
Length
(octets)
Type
Mnemonic
Description
27:26
2
RW
DRX_TUNE4H
Digital Tuning Register
Register file: 0x27 – Digital receiver configuration
, sub-register 0x26 is a 16-bit tuning register. The value
here needs to change depending on the preamble length expected by the receiver. The values required are
given in Table 34. Please take care not to write other values to this register as doing so may cause the
DW1000 to malfunction.
Table 34: Register 0x27:26 DRX_TUNE4H values
Expected Receive Preamble
Length in Symbols
Value to program to
64
0x0010
128 or greater
0x0028