Could you further comment on "The LFSR instruction on the 18C series is
broken, don't use it."?

---
James Newton (PICList Admin #3)
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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Olin Lathrop
Sent: Wednesday, November 15, 2000 09:02
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: FSR


> Whenever someone mentions the FSR (file select register) they
> always seem to quickly [religious reference deleted] and then
> add, "But I would never do it this way".   The FSR seems like
> the obvious way to collect a short frame of data and write
> it to a group of registers in memory.  Is there a dark side
> of this mechanism I need to know about?

It is more efficient to address the register directly when you know which
ones they are specifically.  FSR is the only means to access buffers,
arrays, etc.

The dark sides of FSR are:

1 - You have to remember to save/restore FSR in the interrupt routine if you
use it in the interrupt routine and in the main code.

2 - You have to make sure the indirect register bank setting is correct,
which is different from the direct register bank setting on 16C parts.

3 - The LFSR instruction on the 18C series is broken, don't use it.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@cognivis.com, http://www.cognivis.com

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