RXPACC Adjustment Clarification

My question is to clarify the RXPACC adjustment process outlined in Table18: RXPACC Adjustments by SFD code and the description of the RXPACC register in the DW1000 user manual.

My question is simple: Should I add or subtract the final calculated values in Table 18?

The RXPACC description doesn’t read clearly to me which one it is. For example if I’m using 110K data rate and the special Decawave SFD, then my “Adjustment to RXPACC” value is -82. Is the correct equation

newPreamCount = rxPreamCount + -82

OR

newPreamCount = rxPreamCount - -82

From reading the description it seems like the second - since the SFD is mostly negative symbols then I need increase my accumulator count to correct for it. But the language “Because the SFD sequences contain positive symbols (normal preamble symbols) and negative symbols (symbols which are inverted versions of preamble symbols) which have been added into the channel estimate, add the number of positive symbols and subtract the number of negative symbols in the SFD sequence from the RXPACC count” seems to contradict this.

Can someone please clarify?

Hi
Please check the IC usermanual and see RXPACC field description. It is described there, you can’t miss it.
The field description is just there before the table 18, from where you got your value -82.

So the adjustment is RXPACC + Adjustment. e.g. Adjustment = -5. Then RXPACCnew = RXPACC - 5.

Leo