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<H2><A NAME="SECTION00494000000000000000">
3.9.4 Z80 Interrupt Service Routines</A>
</H2>
<P>
The Z80<A NAME="1751"></A> uses several different methods for determining
the correct interrupt<A NAME="1752"></A> vector depending on the
hardware implementation. Therefore, SDCC ignores the optional interrupt
number and does not attempt to generate an interrupt vector table.
<P>
By default, SDCC generates code for a maskable interrupt, which uses
a RETI instruction to return from the interrupt. To write an interrupt
handler for the non-maskable interrupt, which needs a RETN instruction
instead, add the <I>critical</I> keyword:
<BLOCKQUOTE>
<TT>void nmi_isr (void) critical interrupt</TT>
<BR><TT>{ </TT>
<BR><TT> ... </TT>
<BR><TT>}</TT>
</BLOCKQUOTE>
However if you need to create a non-interruptable interrupt service
routine you would also require the <I>critical</I> keyword. To distinguish
between this and an nmi_isr you must provide an interrupt number.
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2011-03-20
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