[sdiy] IIR Shift Filter problem - help with bug spotting in PIC ASM

[Scott Gravenhorst]

This is a complaint I've also had about much of Microchip's documentation.  I love the
parts they make, but they could do better with documentation clarity.

steve at bendentech.co.uk wrote:
>You are right. The datasheet description of the STATUS register is a bit =
>
>misleading. It says:
>
>"If the STATUS register is the destination for an instruction that =
>
>affects the Z, DC or C bits, then the write to these three bits is
>disabled."
>
>Because XORWF only affects the Z bit, a natural assumption is that the C =
>
>and CD bits should still be accessible (helped by the Instruction Set =
>
>Summary labelling the relevant column as "Status Affected", implying =
>
>that those not listed are not affected).
>
>However, it would appear that what they should have said is:
>
>"If the STATUS register is the destination for an instruction that =
>
>affects ANY OF the Z, DC or C bits, then the write to ALL THREE bits is =
>
>disabled."
>
>i.e. because the XORWF is affecting Z, writes to Z, DC and C are all =
>
>blocked.
>
>The more I read it now, the more obvious it is, but it wasn't obvious =
>
>before!
>
>Yey! I can stop thinking about this now :-)
>
>Steve L.


-- ScottG
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-- Scott Gravenhorst
-- http://scott.joviansynth.com/
-- When the going gets tough, the tough use the command line.
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