I'll document that at the
http://www.sxlist.com
site, but shouldn't that be in the datasheet or errata or somewhere?

---
James Newton
1-619-652-0593
http://www.sxlist.com
mailto:jamesnewton@geocities.com

-----Original Message-----
From: Stephen Holland [mailto:stephen.holland@scenix.com]
Sent: Tuesday, October 17, 2000 11:21
To: 'sxtech@egroups.com'
Subject: RE: [sxtech] [SX]: math or load of PC ALWAYs clears PC.8?
Importance: Low


Correct, JMP PC+W can only be performed in the first half of a page.

Stephen

> -----Original Message-----
> From: James Newton [mailto:jamesnewton@piclist.com]
> Sent: Tuesday, October 17, 2000 11:21 AM
> To: Sxtech@Egroups. Com
> Subject: [sxtech] [SX]: math or load of PC ALWAYs clears PC.8?
>
>
> Ok, here is what I know...
>
> 1. When executing a jmp PC+W, on the SX 18,28,etc.. no carry
> of the addition
> from bit 7 to bit 8 of the PC is performed. This means that
> relative jumps
> are restricted to the half page of 256 instructions from
> which the jump
> originates. Understood, well documented.
>
> 2. The call instruction clears the 9th bit (bit 8) of the PC
> so you can only
> call into the first 256 instruction half page of each 512
> instruction page.
> Understood, well documented.
>
> Now, here is the one I want to make sure I'm not missing
> something on...
>
> 3. As far as I can tell, despite this not being documented
> anywhere, adding,
> or-ing, and-ing, moving, etc... an 8 bit value to the PC
> (bits 0..7) also
> results in CLEARING the 9th bit (bit 8) of the PC. So you can only do
> relative or computed jumps into the first half page of each
> page. Just like
> calls.
>
> Can some one confirm that? or correct me on that point? or
> point me to where
> that third point (and not the first two points) are
> documented by ANYONE?
>
> The main thing that concerns me is that the documentation
> doesn't appear to
> me to make that clear. Please prove me wrong.
>
> ---
> James Newton
> 1-619-652-0593
> http://www.sxlist.com
> mailto:jamesnewton@geocities.com
>
>
>
>
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>
> Parallax SX tech support:   (916) 624-8333
>
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>
>
>

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