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<H2><A NAME="SECTION005612000000000000000">
4.6.12 Stack</A>
</H2>

<P>
The stack<A NAME="3284"></A> implementation for the PIC16 port uses
two indirect registers, FSR1 and FSR2.
<DL>
<DT><STRONG>FSR1</STRONG></DT>
<DD>is assigned as stack pointer
</DD>
<DT><STRONG>FSR2</STRONG></DT>
<DD>is assigned as frame pointer
</DD>
</DL>
The following stack models are supported by the PIC16 port

<UL>
<LI><SMALL>SMALL</SMALL> model
</LI>
<LI><SMALL>LARGE</SMALL> model
</LI>
</UL>
S<SMALL>MALL</SMALL> model means that only the FSRxL byte is used to access
stack and frame, while <I><SMALL>LARGE</SMALL></I> uses both FSRxL and FSRxH
registers. The following table shows the stack/frame pointers sizes
according to stack model and the maximum space they can address:

<P>
<DIV ALIGN="CENTER">
<TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER">Stack &amp; Frame pointer sizes according to stack model</TD>
<TD ALIGN="CENTER">small</TD>
<TD ALIGN="CENTER">large</TD>
</TR>
<TR><TD ALIGN="CENTER">Stack pointer FSR1</TD>
<TD ALIGN="CENTER">8-bits</TD>
<TD ALIGN="CENTER">16-bits</TD>
</TR>
<TR><TD ALIGN="CENTER">Frame pointer FSR2</TD>
<TD ALIGN="CENTER">8-bits</TD>
<TD ALIGN="CENTER">16-bits</TD>
</TR>
</TABLE>
</DIV>
<P>
<DIV ALIGN="CENTER">
</DIV>

<P>
L<SMALL>ARGE </SMALL>stack model is currently not working properly
throughout the code generator. So its use is not advised. Also there
are some other points that need special care:

<OL>
<LI>Do not create stack sections with size more than one physical bank
(that is 256 bytes)
</LI>
<LI>Stack sections should no cross physical bank limits (i.e. #pragma
stack 0x50 0x100)
</LI>
</OL>
These limitations are caused by the fact that only FSRxL is modified
when using SMALL stack model, so no more than 256 bytes of stack can
be used. This problem will disappear after LARGE model is fully implemented.

<P>
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2011-03-20
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