Gotchas: Difference between revisions
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Unfortunately, this means that instructions like <code>OTIR</code> and <code>INIR</code> aren't always useful, since the B register is performing double duty as the high byte of the port and the loop counter. Which means that your port destination on systems with 16-bit ports is constantly moving! Not good!
===RET/RETI/RETN===
Here's one I didn't learn until recently. Depending on the wiring, <code>RETI</code> (return and enable interrupts) and <code>RETN</code> (return from Non-Maskable Interrupt) may end up functioning the same as a normal <code>RET</code>. This means that sometimes you have to use the following (which just makes anyone else reading your code think that you don't know what <code>RETI</code> does.)
<lang z80>EI ;RETI doesn't enable interrupts on this Z80.
RET</lang>
Fortunately, there's a bit of a "reverse gotcha" that helps us out. When interrupts are enabled with <code>EI</code>, there is no chance that an interrupt will occur during the next instruction. <code>EI</code> doesn't actually enable interrupts until the instruction ''after'' it is finished.
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