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

[Tom Wiltshire]

Oh, I dunno so much, Scott. I've found their documentation pretty good in general. When you actually dig into it, it's there in black and white as Steve posted. The problem is *finding* the exact little sub-paragraph that deals with whatever issue you're looking at without losing two days doing it!
I suppose there's a there's a trade-off between "detailed" and "concise". That's a tough balance to find.

On 10 Mar 2017, at 16:11, Scott Gravenhorst <music.maker at gte.net> wrote:

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