On Sun, Sep 02, 2001 at 07:31:59PM -0400, Brandon Fosdick wrote:
[...]
>
> I was trying to use the following function I found on piclist.org
>
> two2n
>         andlw   0x07
>         addwf   PCL, f
>         retlw   0x01
>         retlw   0x02
>         retlw   0x04
>         retlw   0x08
>         retlw   0x10
>         retlw   0x20
>         retlw   0x40
>         retlw   0x80
>
> Nothing complicated. But I've found that if I use the SPI module a
> certain number of times before calling that function, the PIC will
> reset. Eventually I got the number pegged at 18, that is, send/receive
> 18 bytes over the SPI port, then do anything that involves modifying PCL
> and the chip will reset. Sometimes, at around 12 bytes, the chip will
> start executing random instructions, but won't fully reset.
>
> So I thought I had found the two magic numbers to avoid. To my suprise,
> I found that if I change the number of instructions between the SPI
> calls and the PCL modifying instructions, the magic numbers change.
> Fewer instructions, more calls to SPI, and vice-versa.
[...]
Are you sure, that your "two2n" does not cross the page boundary?
Read:
http://www.piclist.com/techref/microchip/tables.htm
http://www.piclist.com/techref/microchip/pages.htm
to get more detailed info.

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