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'[SX]: math or load of PC ALWAYs clears PC.8?'
2000\10\17@141423 by jamesnewton

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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
spam_OUTjamesnewtonTakeThisOuTspamgeocities.com

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2000\10\17@143640 by jamesnewton

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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
jamesnewtonspamKILLspamgeocities.com

{Original Message removed}

2000\10\17@153530 by jamesnewton

face picon face
That's all great documentation of points 1 and 2 in my post. It does NOT
address point 3, which appears to be completely undocumented.

{Original Message removed}

2000\10\21@044800 by James Newton

face picon face
Thanks for that.

Seems like this was something that the SX doc's people "assumed" everyone
would know since the SX is 5x compatible.

James Newton
1-619-652-0593
http://www.sxlist.com
.....jamesnewtonKILLspamspam.....geocities.com


{Original Message removed}

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